1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * BPF extensible scheduler class: Documentation/scheduler/sched-ext.rst 4 * 5 * Built-in idle CPU tracking policy. 6 * 7 * Copyright (c) 2022 Meta Platforms, Inc. and affiliates. 8 * Copyright (c) 2022 Tejun Heo <tj@kernel.org> 9 * Copyright (c) 2022 David Vernet <dvernet@meta.com> 10 * Copyright (c) 2024 Andrea Righi <arighi@nvidia.com> 11 */ 12 #include "ext_idle.h" 13 14 /* Enable/disable built-in idle CPU selection policy */ 15 static DEFINE_STATIC_KEY_FALSE(scx_builtin_idle_enabled); 16 17 /* Enable/disable per-node idle cpumasks */ 18 static DEFINE_STATIC_KEY_FALSE(scx_builtin_idle_per_node); 19 20 /* Enable/disable LLC aware optimizations */ 21 static DEFINE_STATIC_KEY_FALSE(scx_selcpu_topo_llc); 22 23 /* Enable/disable NUMA aware optimizations */ 24 static DEFINE_STATIC_KEY_FALSE(scx_selcpu_topo_numa); 25 26 /* 27 * cpumasks to track idle CPUs within each NUMA node. 28 * 29 * If SCX_OPS_BUILTIN_IDLE_PER_NODE is not enabled, a single global cpumask 30 * from is used to track all the idle CPUs in the system. 31 */ 32 struct scx_idle_cpus { 33 cpumask_var_t cpu; 34 cpumask_var_t smt; 35 }; 36 37 /* 38 * Global host-wide idle cpumasks (used when SCX_OPS_BUILTIN_IDLE_PER_NODE 39 * is not enabled). 40 */ 41 static struct scx_idle_cpus scx_idle_global_masks; 42 43 /* 44 * Per-node idle cpumasks. 45 */ 46 static struct scx_idle_cpus **scx_idle_node_masks; 47 48 /* 49 * Local per-CPU cpumasks (used to generate temporary idle cpumasks). 50 */ 51 static DEFINE_PER_CPU(cpumask_var_t, local_idle_cpumask); 52 static DEFINE_PER_CPU(cpumask_var_t, local_llc_idle_cpumask); 53 static DEFINE_PER_CPU(cpumask_var_t, local_numa_idle_cpumask); 54 55 /* 56 * Return the idle masks associated to a target @node. 57 * 58 * NUMA_NO_NODE identifies the global idle cpumask. 59 */ 60 static struct scx_idle_cpus *idle_cpumask(int node) 61 { 62 return node == NUMA_NO_NODE ? &scx_idle_global_masks : scx_idle_node_masks[node]; 63 } 64 65 /* 66 * Returns the NUMA node ID associated with a @cpu, or NUMA_NO_NODE if 67 * per-node idle cpumasks are disabled. 68 */ 69 static int scx_cpu_node_if_enabled(int cpu) 70 { 71 if (!static_branch_maybe(CONFIG_NUMA, &scx_builtin_idle_per_node)) 72 return NUMA_NO_NODE; 73 74 return cpu_to_node(cpu); 75 } 76 77 static bool scx_idle_test_and_clear_cpu(int cpu) 78 { 79 int node = scx_cpu_node_if_enabled(cpu); 80 struct cpumask *idle_cpus = idle_cpumask(node)->cpu; 81 82 #ifdef CONFIG_SCHED_SMT 83 /* 84 * SMT mask should be cleared whether we can claim @cpu or not. The SMT 85 * cluster is not wholly idle either way. This also prevents 86 * scx_pick_idle_cpu() from getting caught in an infinite loop. 87 */ 88 if (sched_smt_active()) { 89 const struct cpumask *smt = cpu_smt_mask(cpu); 90 struct cpumask *idle_smts = idle_cpumask(node)->smt; 91 92 /* 93 * If offline, @cpu is not its own sibling and 94 * scx_pick_idle_cpu() can get caught in an infinite loop as 95 * @cpu is never cleared from the idle SMT mask. Ensure that 96 * @cpu is eventually cleared. 97 * 98 * NOTE: Use cpumask_intersects() and cpumask_test_cpu() to 99 * reduce memory writes, which may help alleviate cache 100 * coherence pressure. 101 */ 102 if (cpumask_intersects(smt, idle_smts)) 103 cpumask_andnot(idle_smts, idle_smts, smt); 104 else if (cpumask_test_cpu(cpu, idle_smts)) 105 __cpumask_clear_cpu(cpu, idle_smts); 106 } 107 #endif 108 109 return cpumask_test_and_clear_cpu(cpu, idle_cpus); 110 } 111 112 /* 113 * Pick an idle CPU in a specific NUMA node. 114 */ 115 static s32 pick_idle_cpu_in_node(const struct cpumask *cpus_allowed, int node, u64 flags) 116 { 117 int cpu; 118 119 retry: 120 if (sched_smt_active()) { 121 cpu = cpumask_any_and_distribute(idle_cpumask(node)->smt, cpus_allowed); 122 if (cpu < nr_cpu_ids) 123 goto found; 124 125 if (flags & SCX_PICK_IDLE_CORE) 126 return -EBUSY; 127 } 128 129 cpu = cpumask_any_and_distribute(idle_cpumask(node)->cpu, cpus_allowed); 130 if (cpu >= nr_cpu_ids) 131 return -EBUSY; 132 133 found: 134 if (scx_idle_test_and_clear_cpu(cpu)) 135 return cpu; 136 else 137 goto retry; 138 } 139 140 #ifdef CONFIG_NUMA 141 /* 142 * Tracks nodes that have not yet been visited when searching for an idle 143 * CPU across all available nodes. 144 */ 145 static DEFINE_PER_CPU(nodemask_t, per_cpu_unvisited); 146 147 /* 148 * Search for an idle CPU across all nodes, excluding @node. 149 */ 150 static s32 pick_idle_cpu_from_online_nodes(const struct cpumask *cpus_allowed, int node, u64 flags) 151 { 152 nodemask_t *unvisited; 153 s32 cpu = -EBUSY; 154 155 preempt_disable(); 156 unvisited = this_cpu_ptr(&per_cpu_unvisited); 157 158 /* 159 * Restrict the search to the online nodes (excluding the current 160 * node that has been visited already). 161 */ 162 nodes_copy(*unvisited, node_states[N_ONLINE]); 163 node_clear(node, *unvisited); 164 165 /* 166 * Traverse all nodes in order of increasing distance, starting 167 * from @node. 168 * 169 * This loop is O(N^2), with N being the amount of NUMA nodes, 170 * which might be quite expensive in large NUMA systems. However, 171 * this complexity comes into play only when a scheduler enables 172 * SCX_OPS_BUILTIN_IDLE_PER_NODE and it's requesting an idle CPU 173 * without specifying a target NUMA node, so it shouldn't be a 174 * bottleneck is most cases. 175 * 176 * As a future optimization we may want to cache the list of nodes 177 * in a per-node array, instead of actually traversing them every 178 * time. 179 */ 180 for_each_node_numadist(node, *unvisited) { 181 cpu = pick_idle_cpu_in_node(cpus_allowed, node, flags); 182 if (cpu >= 0) 183 break; 184 } 185 preempt_enable(); 186 187 return cpu; 188 } 189 #else 190 static inline s32 191 pick_idle_cpu_from_online_nodes(const struct cpumask *cpus_allowed, int node, u64 flags) 192 { 193 return -EBUSY; 194 } 195 #endif 196 197 /* 198 * Find an idle CPU in the system, starting from @node. 199 */ 200 static s32 scx_pick_idle_cpu(const struct cpumask *cpus_allowed, int node, u64 flags) 201 { 202 s32 cpu; 203 204 /* 205 * Always search in the starting node first (this is an 206 * optimization that can save some cycles even when the search is 207 * not limited to a single node). 208 */ 209 cpu = pick_idle_cpu_in_node(cpus_allowed, node, flags); 210 if (cpu >= 0) 211 return cpu; 212 213 /* 214 * Stop the search if we are using only a single global cpumask 215 * (NUMA_NO_NODE) or if the search is restricted to the first node 216 * only. 217 */ 218 if (node == NUMA_NO_NODE || flags & SCX_PICK_IDLE_IN_NODE) 219 return -EBUSY; 220 221 /* 222 * Extend the search to the other online nodes. 223 */ 224 return pick_idle_cpu_from_online_nodes(cpus_allowed, node, flags); 225 } 226 227 /* 228 * Return the amount of CPUs in the same LLC domain of @cpu (or zero if the LLC 229 * domain is not defined). 230 */ 231 static unsigned int llc_weight(s32 cpu) 232 { 233 struct sched_domain *sd; 234 235 sd = rcu_dereference(per_cpu(sd_llc, cpu)); 236 if (!sd) 237 return 0; 238 239 return sd->span_weight; 240 } 241 242 /* 243 * Return the cpumask representing the LLC domain of @cpu (or NULL if the LLC 244 * domain is not defined). 245 */ 246 static struct cpumask *llc_span(s32 cpu) 247 { 248 struct sched_domain *sd; 249 250 sd = rcu_dereference(per_cpu(sd_llc, cpu)); 251 if (!sd) 252 return NULL; 253 254 return sched_domain_span(sd); 255 } 256 257 /* 258 * Return the amount of CPUs in the same NUMA domain of @cpu (or zero if the 259 * NUMA domain is not defined). 260 */ 261 static unsigned int numa_weight(s32 cpu) 262 { 263 struct sched_domain *sd; 264 struct sched_group *sg; 265 266 sd = rcu_dereference(per_cpu(sd_numa, cpu)); 267 if (!sd) 268 return 0; 269 sg = sd->groups; 270 if (!sg) 271 return 0; 272 273 return sg->group_weight; 274 } 275 276 /* 277 * Return the cpumask representing the NUMA domain of @cpu (or NULL if the NUMA 278 * domain is not defined). 279 */ 280 static struct cpumask *numa_span(s32 cpu) 281 { 282 struct sched_domain *sd; 283 struct sched_group *sg; 284 285 sd = rcu_dereference(per_cpu(sd_numa, cpu)); 286 if (!sd) 287 return NULL; 288 sg = sd->groups; 289 if (!sg) 290 return NULL; 291 292 return sched_group_span(sg); 293 } 294 295 /* 296 * Return true if the LLC domains do not perfectly overlap with the NUMA 297 * domains, false otherwise. 298 */ 299 static bool llc_numa_mismatch(void) 300 { 301 int cpu; 302 303 /* 304 * We need to scan all online CPUs to verify whether their scheduling 305 * domains overlap. 306 * 307 * While it is rare to encounter architectures with asymmetric NUMA 308 * topologies, CPU hotplugging or virtualized environments can result 309 * in asymmetric configurations. 310 * 311 * For example: 312 * 313 * NUMA 0: 314 * - LLC 0: cpu0..cpu7 315 * - LLC 1: cpu8..cpu15 [offline] 316 * 317 * NUMA 1: 318 * - LLC 0: cpu16..cpu23 319 * - LLC 1: cpu24..cpu31 320 * 321 * In this case, if we only check the first online CPU (cpu0), we might 322 * incorrectly assume that the LLC and NUMA domains are fully 323 * overlapping, which is incorrect (as NUMA 1 has two distinct LLC 324 * domains). 325 */ 326 for_each_online_cpu(cpu) 327 if (llc_weight(cpu) != numa_weight(cpu)) 328 return true; 329 330 return false; 331 } 332 333 /* 334 * Initialize topology-aware scheduling. 335 * 336 * Detect if the system has multiple LLC or multiple NUMA domains and enable 337 * cache-aware / NUMA-aware scheduling optimizations in the default CPU idle 338 * selection policy. 339 * 340 * Assumption: the kernel's internal topology representation assumes that each 341 * CPU belongs to a single LLC domain, and that each LLC domain is entirely 342 * contained within a single NUMA node. 343 */ 344 void scx_idle_update_selcpu_topology(struct sched_ext_ops *ops) 345 { 346 bool enable_llc = false, enable_numa = false; 347 unsigned int nr_cpus; 348 s32 cpu = cpumask_first(cpu_online_mask); 349 350 /* 351 * Enable LLC domain optimization only when there are multiple LLC 352 * domains among the online CPUs. If all online CPUs are part of a 353 * single LLC domain, the idle CPU selection logic can choose any 354 * online CPU without bias. 355 * 356 * Note that it is sufficient to check the LLC domain of the first 357 * online CPU to determine whether a single LLC domain includes all 358 * CPUs. 359 */ 360 rcu_read_lock(); 361 nr_cpus = llc_weight(cpu); 362 if (nr_cpus > 0) { 363 if (nr_cpus < num_online_cpus()) 364 enable_llc = true; 365 pr_debug("sched_ext: LLC=%*pb weight=%u\n", 366 cpumask_pr_args(llc_span(cpu)), llc_weight(cpu)); 367 } 368 369 /* 370 * Enable NUMA optimization only when there are multiple NUMA domains 371 * among the online CPUs and the NUMA domains don't perfectly overlaps 372 * with the LLC domains. 373 * 374 * If all CPUs belong to the same NUMA node and the same LLC domain, 375 * enabling both NUMA and LLC optimizations is unnecessary, as checking 376 * for an idle CPU in the same domain twice is redundant. 377 * 378 * If SCX_OPS_BUILTIN_IDLE_PER_NODE is enabled ignore the NUMA 379 * optimization, as we would naturally select idle CPUs within 380 * specific NUMA nodes querying the corresponding per-node cpumask. 381 */ 382 if (!(ops->flags & SCX_OPS_BUILTIN_IDLE_PER_NODE)) { 383 nr_cpus = numa_weight(cpu); 384 if (nr_cpus > 0) { 385 if (nr_cpus < num_online_cpus() && llc_numa_mismatch()) 386 enable_numa = true; 387 pr_debug("sched_ext: NUMA=%*pb weight=%u\n", 388 cpumask_pr_args(numa_span(cpu)), nr_cpus); 389 } 390 } 391 rcu_read_unlock(); 392 393 pr_debug("sched_ext: LLC idle selection %s\n", 394 str_enabled_disabled(enable_llc)); 395 pr_debug("sched_ext: NUMA idle selection %s\n", 396 str_enabled_disabled(enable_numa)); 397 398 if (enable_llc) 399 static_branch_enable_cpuslocked(&scx_selcpu_topo_llc); 400 else 401 static_branch_disable_cpuslocked(&scx_selcpu_topo_llc); 402 if (enable_numa) 403 static_branch_enable_cpuslocked(&scx_selcpu_topo_numa); 404 else 405 static_branch_disable_cpuslocked(&scx_selcpu_topo_numa); 406 } 407 408 /* 409 * Return true if @p can run on all possible CPUs, false otherwise. 410 */ 411 static inline bool task_affinity_all(const struct task_struct *p) 412 { 413 return p->nr_cpus_allowed >= num_possible_cpus(); 414 } 415 416 /* 417 * Built-in CPU idle selection policy: 418 * 419 * 1. Prioritize full-idle cores: 420 * - always prioritize CPUs from fully idle cores (both logical CPUs are 421 * idle) to avoid interference caused by SMT. 422 * 423 * 2. Reuse the same CPU: 424 * - prefer the last used CPU to take advantage of cached data (L1, L2) and 425 * branch prediction optimizations. 426 * 427 * 3. Pick a CPU within the same LLC (Last-Level Cache): 428 * - if the above conditions aren't met, pick a CPU that shares the same 429 * LLC, if the LLC domain is a subset of @cpus_allowed, to maintain 430 * cache locality. 431 * 432 * 4. Pick a CPU within the same NUMA node, if enabled: 433 * - choose a CPU from the same NUMA node, if the node cpumask is a 434 * subset of @cpus_allowed, to reduce memory access latency. 435 * 436 * 5. Pick any idle CPU within the @cpus_allowed domain. 437 * 438 * Step 3 and 4 are performed only if the system has, respectively, 439 * multiple LLCs / multiple NUMA nodes (see scx_selcpu_topo_llc and 440 * scx_selcpu_topo_numa) and they don't contain the same subset of CPUs. 441 * 442 * If %SCX_OPS_BUILTIN_IDLE_PER_NODE is enabled, the search will always 443 * begin in @prev_cpu's node and proceed to other nodes in order of 444 * increasing distance. 445 * 446 * Return the picked CPU if idle, or a negative value otherwise. 447 * 448 * NOTE: tasks that can only run on 1 CPU are excluded by this logic, because 449 * we never call ops.select_cpu() for them, see select_task_rq(). 450 */ 451 s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu, u64 wake_flags, 452 const struct cpumask *cpus_allowed, u64 flags) 453 { 454 const struct cpumask *llc_cpus = NULL, *numa_cpus = NULL; 455 const struct cpumask *allowed = cpus_allowed ?: p->cpus_ptr; 456 int node = scx_cpu_node_if_enabled(prev_cpu); 457 bool is_prev_allowed; 458 s32 cpu; 459 460 preempt_disable(); 461 462 /* 463 * Check whether @prev_cpu is still within the allowed set. If not, 464 * we can still try selecting a nearby CPU. 465 */ 466 is_prev_allowed = cpumask_test_cpu(prev_cpu, allowed); 467 468 /* 469 * Determine the subset of CPUs usable by @p within @cpus_allowed. 470 */ 471 if (allowed != p->cpus_ptr) { 472 struct cpumask *local_cpus = this_cpu_cpumask_var_ptr(local_idle_cpumask); 473 474 if (task_affinity_all(p)) { 475 allowed = cpus_allowed; 476 } else if (cpumask_and(local_cpus, cpus_allowed, p->cpus_ptr)) { 477 allowed = local_cpus; 478 } else { 479 cpu = -EBUSY; 480 goto out_enable; 481 } 482 } 483 484 /* 485 * This is necessary to protect llc_cpus. 486 */ 487 rcu_read_lock(); 488 489 /* 490 * Determine the subset of CPUs that the task can use in its 491 * current LLC and node. 492 * 493 * If the task can run on all CPUs, use the node and LLC cpumasks 494 * directly. 495 */ 496 if (static_branch_maybe(CONFIG_NUMA, &scx_selcpu_topo_numa)) { 497 struct cpumask *local_cpus = this_cpu_cpumask_var_ptr(local_numa_idle_cpumask); 498 const struct cpumask *cpus = numa_span(prev_cpu); 499 500 if (allowed == p->cpus_ptr && task_affinity_all(p)) 501 numa_cpus = cpus; 502 else if (cpus && cpumask_and(local_cpus, allowed, cpus)) 503 numa_cpus = local_cpus; 504 } 505 506 if (static_branch_maybe(CONFIG_SCHED_MC, &scx_selcpu_topo_llc)) { 507 struct cpumask *local_cpus = this_cpu_cpumask_var_ptr(local_llc_idle_cpumask); 508 const struct cpumask *cpus = llc_span(prev_cpu); 509 510 if (allowed == p->cpus_ptr && task_affinity_all(p)) 511 llc_cpus = cpus; 512 else if (cpus && cpumask_and(local_cpus, allowed, cpus)) 513 llc_cpus = local_cpus; 514 } 515 516 /* 517 * If WAKE_SYNC, try to migrate the wakee to the waker's CPU. 518 */ 519 if (wake_flags & SCX_WAKE_SYNC) { 520 int waker_node; 521 522 /* 523 * If the waker's CPU is cache affine and prev_cpu is idle, 524 * then avoid a migration. 525 */ 526 cpu = smp_processor_id(); 527 if (is_prev_allowed && cpus_share_cache(cpu, prev_cpu) && 528 scx_idle_test_and_clear_cpu(prev_cpu)) { 529 cpu = prev_cpu; 530 goto out_unlock; 531 } 532 533 /* 534 * If the waker's local DSQ is empty, and the system is under 535 * utilized, try to wake up @p to the local DSQ of the waker. 536 * 537 * Checking only for an empty local DSQ is insufficient as it 538 * could give the wakee an unfair advantage when the system is 539 * oversaturated. 540 * 541 * Checking only for the presence of idle CPUs is also 542 * insufficient as the local DSQ of the waker could have tasks 543 * piled up on it even if there is an idle core elsewhere on 544 * the system. 545 */ 546 waker_node = cpu_to_node(cpu); 547 if (!(current->flags & PF_EXITING) && 548 cpu_rq(cpu)->scx.local_dsq.nr == 0 && 549 (!(flags & SCX_PICK_IDLE_IN_NODE) || (waker_node == node)) && 550 !cpumask_empty(idle_cpumask(waker_node)->cpu)) { 551 if (cpumask_test_cpu(cpu, allowed)) 552 goto out_unlock; 553 } 554 } 555 556 /* 557 * If CPU has SMT, any wholly idle CPU is likely a better pick than 558 * partially idle @prev_cpu. 559 */ 560 if (sched_smt_active()) { 561 /* 562 * Keep using @prev_cpu if it's part of a fully idle core. 563 */ 564 if (is_prev_allowed && 565 cpumask_test_cpu(prev_cpu, idle_cpumask(node)->smt) && 566 scx_idle_test_and_clear_cpu(prev_cpu)) { 567 cpu = prev_cpu; 568 goto out_unlock; 569 } 570 571 /* 572 * Search for any fully idle core in the same LLC domain. 573 */ 574 if (llc_cpus) { 575 cpu = pick_idle_cpu_in_node(llc_cpus, node, SCX_PICK_IDLE_CORE); 576 if (cpu >= 0) 577 goto out_unlock; 578 } 579 580 /* 581 * Search for any fully idle core in the same NUMA node. 582 */ 583 if (numa_cpus) { 584 cpu = pick_idle_cpu_in_node(numa_cpus, node, SCX_PICK_IDLE_CORE); 585 if (cpu >= 0) 586 goto out_unlock; 587 } 588 589 /* 590 * Search for any full-idle core usable by the task. 591 * 592 * If the node-aware idle CPU selection policy is enabled 593 * (%SCX_OPS_BUILTIN_IDLE_PER_NODE), the search will always 594 * begin in prev_cpu's node and proceed to other nodes in 595 * order of increasing distance. 596 */ 597 cpu = scx_pick_idle_cpu(allowed, node, flags | SCX_PICK_IDLE_CORE); 598 if (cpu >= 0) 599 goto out_unlock; 600 601 /* 602 * Give up if we're strictly looking for a full-idle SMT 603 * core. 604 */ 605 if (flags & SCX_PICK_IDLE_CORE) { 606 cpu = -EBUSY; 607 goto out_unlock; 608 } 609 } 610 611 /* 612 * Use @prev_cpu if it's idle. 613 */ 614 if (is_prev_allowed && scx_idle_test_and_clear_cpu(prev_cpu)) { 615 cpu = prev_cpu; 616 goto out_unlock; 617 } 618 619 /* 620 * Search for any idle CPU in the same LLC domain. 621 */ 622 if (llc_cpus) { 623 cpu = pick_idle_cpu_in_node(llc_cpus, node, 0); 624 if (cpu >= 0) 625 goto out_unlock; 626 } 627 628 /* 629 * Search for any idle CPU in the same NUMA node. 630 */ 631 if (numa_cpus) { 632 cpu = pick_idle_cpu_in_node(numa_cpus, node, 0); 633 if (cpu >= 0) 634 goto out_unlock; 635 } 636 637 /* 638 * Search for any idle CPU usable by the task. 639 * 640 * If the node-aware idle CPU selection policy is enabled 641 * (%SCX_OPS_BUILTIN_IDLE_PER_NODE), the search will always begin 642 * in prev_cpu's node and proceed to other nodes in order of 643 * increasing distance. 644 */ 645 cpu = scx_pick_idle_cpu(allowed, node, flags); 646 647 out_unlock: 648 rcu_read_unlock(); 649 out_enable: 650 preempt_enable(); 651 652 return cpu; 653 } 654 655 /* 656 * Initialize global and per-node idle cpumasks. 657 */ 658 void scx_idle_init_masks(void) 659 { 660 int i; 661 662 /* Allocate global idle cpumasks */ 663 BUG_ON(!alloc_cpumask_var(&scx_idle_global_masks.cpu, GFP_KERNEL)); 664 BUG_ON(!alloc_cpumask_var(&scx_idle_global_masks.smt, GFP_KERNEL)); 665 666 /* Allocate per-node idle cpumasks */ 667 scx_idle_node_masks = kcalloc(num_possible_nodes(), 668 sizeof(*scx_idle_node_masks), GFP_KERNEL); 669 BUG_ON(!scx_idle_node_masks); 670 671 for_each_node(i) { 672 scx_idle_node_masks[i] = kzalloc_node(sizeof(**scx_idle_node_masks), 673 GFP_KERNEL, i); 674 BUG_ON(!scx_idle_node_masks[i]); 675 676 BUG_ON(!alloc_cpumask_var_node(&scx_idle_node_masks[i]->cpu, GFP_KERNEL, i)); 677 BUG_ON(!alloc_cpumask_var_node(&scx_idle_node_masks[i]->smt, GFP_KERNEL, i)); 678 } 679 680 /* Allocate local per-cpu idle cpumasks */ 681 for_each_possible_cpu(i) { 682 BUG_ON(!alloc_cpumask_var_node(&per_cpu(local_idle_cpumask, i), 683 GFP_KERNEL, cpu_to_node(i))); 684 BUG_ON(!alloc_cpumask_var_node(&per_cpu(local_llc_idle_cpumask, i), 685 GFP_KERNEL, cpu_to_node(i))); 686 BUG_ON(!alloc_cpumask_var_node(&per_cpu(local_numa_idle_cpumask, i), 687 GFP_KERNEL, cpu_to_node(i))); 688 } 689 } 690 691 static void update_builtin_idle(int cpu, bool idle) 692 { 693 int node = scx_cpu_node_if_enabled(cpu); 694 struct cpumask *idle_cpus = idle_cpumask(node)->cpu; 695 696 assign_cpu(cpu, idle_cpus, idle); 697 698 #ifdef CONFIG_SCHED_SMT 699 if (sched_smt_active()) { 700 const struct cpumask *smt = cpu_smt_mask(cpu); 701 struct cpumask *idle_smts = idle_cpumask(node)->smt; 702 703 if (idle) { 704 /* 705 * idle_smt handling is racy but that's fine as it's 706 * only for optimization and self-correcting. 707 */ 708 if (!cpumask_subset(smt, idle_cpus)) 709 return; 710 cpumask_or(idle_smts, idle_smts, smt); 711 } else { 712 cpumask_andnot(idle_smts, idle_smts, smt); 713 } 714 } 715 #endif 716 } 717 718 /* 719 * Update the idle state of a CPU to @idle. 720 * 721 * If @do_notify is true, ops.update_idle() is invoked to notify the scx 722 * scheduler of an actual idle state transition (idle to busy or vice 723 * versa). If @do_notify is false, only the idle state in the idle masks is 724 * refreshed without invoking ops.update_idle(). 725 * 726 * This distinction is necessary, because an idle CPU can be "reserved" and 727 * awakened via scx_bpf_pick_idle_cpu() + scx_bpf_kick_cpu(), marking it as 728 * busy even if no tasks are dispatched. In this case, the CPU may return 729 * to idle without a true state transition. Refreshing the idle masks 730 * without invoking ops.update_idle() ensures accurate idle state tracking 731 * while avoiding unnecessary updates and maintaining balanced state 732 * transitions. 733 */ 734 void __scx_update_idle(struct rq *rq, bool idle, bool do_notify) 735 { 736 struct scx_sched *sch = scx_root; 737 int cpu = cpu_of(rq); 738 739 lockdep_assert_rq_held(rq); 740 741 /* 742 * Update the idle masks: 743 * - for real idle transitions (do_notify == true) 744 * - for idle-to-idle transitions (indicated by the previous task 745 * being the idle thread, managed by pick_task_idle()) 746 * 747 * Skip updating idle masks if the previous task is not the idle 748 * thread, since set_next_task_idle() has already handled it when 749 * transitioning from a task to the idle thread (calling this 750 * function with do_notify == true). 751 * 752 * In this way we can avoid updating the idle masks twice, 753 * unnecessarily. 754 */ 755 if (static_branch_likely(&scx_builtin_idle_enabled)) 756 if (do_notify || is_idle_task(rq->curr)) 757 update_builtin_idle(cpu, idle); 758 759 /* 760 * Trigger ops.update_idle() only when transitioning from a task to 761 * the idle thread and vice versa. 762 * 763 * Idle transitions are indicated by do_notify being set to true, 764 * managed by put_prev_task_idle()/set_next_task_idle(). 765 * 766 * This must come after builtin idle update so that BPF schedulers can 767 * create interlocking between ops.update_idle() and ops.enqueue() - 768 * either enqueue() sees the idle bit or update_idle() sees the task 769 * that enqueue() queued. 770 */ 771 if (SCX_HAS_OP(sch, update_idle) && do_notify && !scx_rq_bypassing(rq)) 772 SCX_CALL_OP(sch, SCX_KF_REST, update_idle, rq, cpu_of(rq), idle); 773 } 774 775 static void reset_idle_masks(struct sched_ext_ops *ops) 776 { 777 int node; 778 779 /* 780 * Consider all online cpus idle. Should converge to the actual state 781 * quickly. 782 */ 783 if (!(ops->flags & SCX_OPS_BUILTIN_IDLE_PER_NODE)) { 784 cpumask_copy(idle_cpumask(NUMA_NO_NODE)->cpu, cpu_online_mask); 785 cpumask_copy(idle_cpumask(NUMA_NO_NODE)->smt, cpu_online_mask); 786 return; 787 } 788 789 for_each_node(node) { 790 const struct cpumask *node_mask = cpumask_of_node(node); 791 792 cpumask_and(idle_cpumask(node)->cpu, cpu_online_mask, node_mask); 793 cpumask_and(idle_cpumask(node)->smt, cpu_online_mask, node_mask); 794 } 795 } 796 797 void scx_idle_enable(struct sched_ext_ops *ops) 798 { 799 if (!ops->update_idle || (ops->flags & SCX_OPS_KEEP_BUILTIN_IDLE)) 800 static_branch_enable_cpuslocked(&scx_builtin_idle_enabled); 801 else 802 static_branch_disable_cpuslocked(&scx_builtin_idle_enabled); 803 804 if (ops->flags & SCX_OPS_BUILTIN_IDLE_PER_NODE) 805 static_branch_enable_cpuslocked(&scx_builtin_idle_per_node); 806 else 807 static_branch_disable_cpuslocked(&scx_builtin_idle_per_node); 808 809 reset_idle_masks(ops); 810 } 811 812 void scx_idle_disable(void) 813 { 814 static_branch_disable(&scx_builtin_idle_enabled); 815 static_branch_disable(&scx_builtin_idle_per_node); 816 } 817 818 /******************************************************************************** 819 * Helpers that can be called from the BPF scheduler. 820 */ 821 822 static int validate_node(struct scx_sched *sch, int node) 823 { 824 if (!static_branch_likely(&scx_builtin_idle_per_node)) { 825 scx_error(sch, "per-node idle tracking is disabled"); 826 return -EOPNOTSUPP; 827 } 828 829 /* Return no entry for NUMA_NO_NODE (not a critical scx error) */ 830 if (node == NUMA_NO_NODE) 831 return -ENOENT; 832 833 /* Make sure node is in a valid range */ 834 if (node < 0 || node >= nr_node_ids) { 835 scx_error(sch, "invalid node %d", node); 836 return -EINVAL; 837 } 838 839 /* Make sure the node is part of the set of possible nodes */ 840 if (!node_possible(node)) { 841 scx_error(sch, "unavailable node %d", node); 842 return -EINVAL; 843 } 844 845 return node; 846 } 847 848 __bpf_kfunc_start_defs(); 849 850 static bool check_builtin_idle_enabled(struct scx_sched *sch) 851 { 852 if (static_branch_likely(&scx_builtin_idle_enabled)) 853 return true; 854 855 scx_error(sch, "built-in idle tracking is disabled"); 856 return false; 857 } 858 859 /* 860 * Determine whether @p is a migration-disabled task in the context of BPF 861 * code. 862 * 863 * We can't simply check whether @p->migration_disabled is set in a 864 * sched_ext callback, because migration is always disabled for the current 865 * task while running BPF code. 866 * 867 * The prolog (__bpf_prog_enter) and epilog (__bpf_prog_exit) respectively 868 * disable and re-enable migration. For this reason, the current task 869 * inside a sched_ext callback is always a migration-disabled task. 870 * 871 * Therefore, when @p->migration_disabled == 1, check whether @p is the 872 * current task or not: if it is, then migration was not disabled before 873 * entering the callback, otherwise migration was disabled. 874 * 875 * Returns true if @p is migration-disabled, false otherwise. 876 */ 877 static bool is_bpf_migration_disabled(const struct task_struct *p) 878 { 879 if (p->migration_disabled == 1) 880 return p != current; 881 else 882 return p->migration_disabled; 883 } 884 885 static s32 select_cpu_from_kfunc(struct scx_sched *sch, struct task_struct *p, 886 s32 prev_cpu, u64 wake_flags, 887 const struct cpumask *allowed, u64 flags) 888 { 889 struct rq *rq; 890 struct rq_flags rf; 891 s32 cpu; 892 893 if (!ops_cpu_valid(sch, prev_cpu, NULL)) 894 return -EINVAL; 895 896 if (!check_builtin_idle_enabled(sch)) 897 return -EBUSY; 898 899 /* 900 * If called from an unlocked context, acquire the task's rq lock, 901 * so that we can safely access p->cpus_ptr and p->nr_cpus_allowed. 902 * 903 * Otherwise, allow to use this kfunc only from ops.select_cpu() 904 * and ops.select_enqueue(). 905 */ 906 if (scx_kf_allowed_if_unlocked()) { 907 rq = task_rq_lock(p, &rf); 908 } else { 909 if (!scx_kf_allowed(sch, SCX_KF_SELECT_CPU | SCX_KF_ENQUEUE)) 910 return -EPERM; 911 rq = scx_locked_rq(); 912 } 913 914 /* 915 * Validate locking correctness to access p->cpus_ptr and 916 * p->nr_cpus_allowed: if we're holding an rq lock, we're safe; 917 * otherwise, assert that p->pi_lock is held. 918 */ 919 if (!rq) 920 lockdep_assert_held(&p->pi_lock); 921 922 /* 923 * This may also be called from ops.enqueue(), so we need to handle 924 * per-CPU tasks as well. For these tasks, we can skip all idle CPU 925 * selection optimizations and simply check whether the previously 926 * used CPU is idle and within the allowed cpumask. 927 */ 928 if (p->nr_cpus_allowed == 1 || is_bpf_migration_disabled(p)) { 929 if (cpumask_test_cpu(prev_cpu, allowed ?: p->cpus_ptr) && 930 scx_idle_test_and_clear_cpu(prev_cpu)) 931 cpu = prev_cpu; 932 else 933 cpu = -EBUSY; 934 } else { 935 cpu = scx_select_cpu_dfl(p, prev_cpu, wake_flags, 936 allowed ?: p->cpus_ptr, flags); 937 } 938 939 if (scx_kf_allowed_if_unlocked()) 940 task_rq_unlock(rq, p, &rf); 941 942 return cpu; 943 } 944 945 /** 946 * scx_bpf_cpu_node - Return the NUMA node the given @cpu belongs to, or 947 * trigger an error if @cpu is invalid 948 * @cpu: target CPU 949 */ 950 __bpf_kfunc int scx_bpf_cpu_node(s32 cpu) 951 { 952 struct scx_sched *sch; 953 954 guard(rcu)(); 955 956 sch = rcu_dereference(scx_root); 957 if (unlikely(!sch) || !ops_cpu_valid(sch, cpu, NULL)) 958 return NUMA_NO_NODE; 959 return cpu_to_node(cpu); 960 } 961 962 /** 963 * scx_bpf_select_cpu_dfl - The default implementation of ops.select_cpu() 964 * @p: task_struct to select a CPU for 965 * @prev_cpu: CPU @p was on previously 966 * @wake_flags: %SCX_WAKE_* flags 967 * @is_idle: out parameter indicating whether the returned CPU is idle 968 * 969 * Can be called from ops.select_cpu(), ops.enqueue(), or from an unlocked 970 * context such as a BPF test_run() call, as long as built-in CPU selection 971 * is enabled: ops.update_idle() is missing or %SCX_OPS_KEEP_BUILTIN_IDLE 972 * is set. 973 * 974 * Returns the picked CPU with *@is_idle indicating whether the picked CPU is 975 * currently idle and thus a good candidate for direct dispatching. 976 */ 977 __bpf_kfunc s32 scx_bpf_select_cpu_dfl(struct task_struct *p, s32 prev_cpu, 978 u64 wake_flags, bool *is_idle) 979 { 980 struct scx_sched *sch; 981 s32 cpu; 982 983 guard(rcu)(); 984 985 sch = rcu_dereference(scx_root); 986 if (unlikely(!sch)) 987 return -ENODEV; 988 989 cpu = select_cpu_from_kfunc(sch, p, prev_cpu, wake_flags, NULL, 0); 990 if (cpu >= 0) { 991 *is_idle = true; 992 return cpu; 993 } 994 *is_idle = false; 995 return prev_cpu; 996 } 997 998 /** 999 * scx_bpf_select_cpu_and - Pick an idle CPU usable by task @p, 1000 * prioritizing those in @cpus_allowed 1001 * @p: task_struct to select a CPU for 1002 * @prev_cpu: CPU @p was on previously 1003 * @wake_flags: %SCX_WAKE_* flags 1004 * @cpus_allowed: cpumask of allowed CPUs 1005 * @flags: %SCX_PICK_IDLE* flags 1006 * 1007 * Can be called from ops.select_cpu(), ops.enqueue(), or from an unlocked 1008 * context such as a BPF test_run() call, as long as built-in CPU selection 1009 * is enabled: ops.update_idle() is missing or %SCX_OPS_KEEP_BUILTIN_IDLE 1010 * is set. 1011 * 1012 * @p, @prev_cpu and @wake_flags match ops.select_cpu(). 1013 * 1014 * Returns the selected idle CPU, which will be automatically awakened upon 1015 * returning from ops.select_cpu() and can be used for direct dispatch, or 1016 * a negative value if no idle CPU is available. 1017 */ 1018 __bpf_kfunc s32 scx_bpf_select_cpu_and(struct task_struct *p, s32 prev_cpu, u64 wake_flags, 1019 const struct cpumask *cpus_allowed, u64 flags) 1020 { 1021 struct scx_sched *sch; 1022 1023 guard(rcu)(); 1024 1025 sch = rcu_dereference(scx_root); 1026 if (unlikely(!sch)) 1027 return -ENODEV; 1028 1029 return select_cpu_from_kfunc(sch, p, prev_cpu, wake_flags, 1030 cpus_allowed, flags); 1031 } 1032 1033 /** 1034 * scx_bpf_get_idle_cpumask_node - Get a referenced kptr to the 1035 * idle-tracking per-CPU cpumask of a target NUMA node. 1036 * @node: target NUMA node 1037 * 1038 * Returns an empty cpumask if idle tracking is not enabled, if @node is 1039 * not valid, or running on a UP kernel. In this case the actual error will 1040 * be reported to the BPF scheduler via scx_error(). 1041 */ 1042 __bpf_kfunc const struct cpumask *scx_bpf_get_idle_cpumask_node(int node) 1043 { 1044 struct scx_sched *sch; 1045 1046 guard(rcu)(); 1047 1048 sch = rcu_dereference(scx_root); 1049 if (unlikely(!sch)) 1050 return cpu_none_mask; 1051 1052 node = validate_node(sch, node); 1053 if (node < 0) 1054 return cpu_none_mask; 1055 1056 return idle_cpumask(node)->cpu; 1057 } 1058 1059 /** 1060 * scx_bpf_get_idle_cpumask - Get a referenced kptr to the idle-tracking 1061 * per-CPU cpumask. 1062 * 1063 * Returns an empty mask if idle tracking is not enabled, or running on a 1064 * UP kernel. 1065 */ 1066 __bpf_kfunc const struct cpumask *scx_bpf_get_idle_cpumask(void) 1067 { 1068 struct scx_sched *sch; 1069 1070 guard(rcu)(); 1071 1072 sch = rcu_dereference(scx_root); 1073 if (unlikely(!sch)) 1074 return cpu_none_mask; 1075 1076 if (static_branch_unlikely(&scx_builtin_idle_per_node)) { 1077 scx_error(sch, "SCX_OPS_BUILTIN_IDLE_PER_NODE enabled"); 1078 return cpu_none_mask; 1079 } 1080 1081 if (!check_builtin_idle_enabled(sch)) 1082 return cpu_none_mask; 1083 1084 return idle_cpumask(NUMA_NO_NODE)->cpu; 1085 } 1086 1087 /** 1088 * scx_bpf_get_idle_smtmask_node - Get a referenced kptr to the 1089 * idle-tracking, per-physical-core cpumask of a target NUMA node. Can be 1090 * used to determine if an entire physical core is free. 1091 * @node: target NUMA node 1092 * 1093 * Returns an empty cpumask if idle tracking is not enabled, if @node is 1094 * not valid, or running on a UP kernel. In this case the actual error will 1095 * be reported to the BPF scheduler via scx_error(). 1096 */ 1097 __bpf_kfunc const struct cpumask *scx_bpf_get_idle_smtmask_node(int node) 1098 { 1099 struct scx_sched *sch; 1100 1101 guard(rcu)(); 1102 1103 sch = rcu_dereference(scx_root); 1104 if (unlikely(!sch)) 1105 return cpu_none_mask; 1106 1107 node = validate_node(sch, node); 1108 if (node < 0) 1109 return cpu_none_mask; 1110 1111 if (sched_smt_active()) 1112 return idle_cpumask(node)->smt; 1113 else 1114 return idle_cpumask(node)->cpu; 1115 } 1116 1117 /** 1118 * scx_bpf_get_idle_smtmask - Get a referenced kptr to the idle-tracking, 1119 * per-physical-core cpumask. Can be used to determine if an entire physical 1120 * core is free. 1121 * 1122 * Returns an empty mask if idle tracking is not enabled, or running on a 1123 * UP kernel. 1124 */ 1125 __bpf_kfunc const struct cpumask *scx_bpf_get_idle_smtmask(void) 1126 { 1127 struct scx_sched *sch; 1128 1129 guard(rcu)(); 1130 1131 sch = rcu_dereference(scx_root); 1132 if (unlikely(!sch)) 1133 return cpu_none_mask; 1134 1135 if (static_branch_unlikely(&scx_builtin_idle_per_node)) { 1136 scx_error(sch, "SCX_OPS_BUILTIN_IDLE_PER_NODE enabled"); 1137 return cpu_none_mask; 1138 } 1139 1140 if (!check_builtin_idle_enabled(sch)) 1141 return cpu_none_mask; 1142 1143 if (sched_smt_active()) 1144 return idle_cpumask(NUMA_NO_NODE)->smt; 1145 else 1146 return idle_cpumask(NUMA_NO_NODE)->cpu; 1147 } 1148 1149 /** 1150 * scx_bpf_put_idle_cpumask - Release a previously acquired referenced kptr to 1151 * either the percpu, or SMT idle-tracking cpumask. 1152 * @idle_mask: &cpumask to use 1153 */ 1154 __bpf_kfunc void scx_bpf_put_idle_cpumask(const struct cpumask *idle_mask) 1155 { 1156 /* 1157 * Empty function body because we aren't actually acquiring or releasing 1158 * a reference to a global idle cpumask, which is read-only in the 1159 * caller and is never released. The acquire / release semantics here 1160 * are just used to make the cpumask a trusted pointer in the caller. 1161 */ 1162 } 1163 1164 /** 1165 * scx_bpf_test_and_clear_cpu_idle - Test and clear @cpu's idle state 1166 * @cpu: cpu to test and clear idle for 1167 * 1168 * Returns %true if @cpu was idle and its idle state was successfully cleared. 1169 * %false otherwise. 1170 * 1171 * Unavailable if ops.update_idle() is implemented and 1172 * %SCX_OPS_KEEP_BUILTIN_IDLE is not set. 1173 */ 1174 __bpf_kfunc bool scx_bpf_test_and_clear_cpu_idle(s32 cpu) 1175 { 1176 struct scx_sched *sch; 1177 1178 guard(rcu)(); 1179 1180 sch = rcu_dereference(scx_root); 1181 if (unlikely(!sch)) 1182 return false; 1183 1184 if (!check_builtin_idle_enabled(sch)) 1185 return false; 1186 1187 if (!ops_cpu_valid(sch, cpu, NULL)) 1188 return false; 1189 1190 return scx_idle_test_and_clear_cpu(cpu); 1191 } 1192 1193 /** 1194 * scx_bpf_pick_idle_cpu_node - Pick and claim an idle cpu from @node 1195 * @cpus_allowed: Allowed cpumask 1196 * @node: target NUMA node 1197 * @flags: %SCX_PICK_IDLE_* flags 1198 * 1199 * Pick and claim an idle cpu in @cpus_allowed from the NUMA node @node. 1200 * 1201 * Returns the picked idle cpu number on success, or -%EBUSY if no matching 1202 * cpu was found. 1203 * 1204 * The search starts from @node and proceeds to other online NUMA nodes in 1205 * order of increasing distance (unless SCX_PICK_IDLE_IN_NODE is specified, 1206 * in which case the search is limited to the target @node). 1207 * 1208 * Always returns an error if ops.update_idle() is implemented and 1209 * %SCX_OPS_KEEP_BUILTIN_IDLE is not set, or if 1210 * %SCX_OPS_BUILTIN_IDLE_PER_NODE is not set. 1211 */ 1212 __bpf_kfunc s32 scx_bpf_pick_idle_cpu_node(const struct cpumask *cpus_allowed, 1213 int node, u64 flags) 1214 { 1215 struct scx_sched *sch; 1216 1217 guard(rcu)(); 1218 1219 sch = rcu_dereference(scx_root); 1220 if (unlikely(!sch)) 1221 return -ENODEV; 1222 1223 node = validate_node(sch, node); 1224 if (node < 0) 1225 return node; 1226 1227 return scx_pick_idle_cpu(cpus_allowed, node, flags); 1228 } 1229 1230 /** 1231 * scx_bpf_pick_idle_cpu - Pick and claim an idle cpu 1232 * @cpus_allowed: Allowed cpumask 1233 * @flags: %SCX_PICK_IDLE_CPU_* flags 1234 * 1235 * Pick and claim an idle cpu in @cpus_allowed. Returns the picked idle cpu 1236 * number on success. -%EBUSY if no matching cpu was found. 1237 * 1238 * Idle CPU tracking may race against CPU scheduling state transitions. For 1239 * example, this function may return -%EBUSY as CPUs are transitioning into the 1240 * idle state. If the caller then assumes that there will be dispatch events on 1241 * the CPUs as they were all busy, the scheduler may end up stalling with CPUs 1242 * idling while there are pending tasks. Use scx_bpf_pick_any_cpu() and 1243 * scx_bpf_kick_cpu() to guarantee that there will be at least one dispatch 1244 * event in the near future. 1245 * 1246 * Unavailable if ops.update_idle() is implemented and 1247 * %SCX_OPS_KEEP_BUILTIN_IDLE is not set. 1248 * 1249 * Always returns an error if %SCX_OPS_BUILTIN_IDLE_PER_NODE is set, use 1250 * scx_bpf_pick_idle_cpu_node() instead. 1251 */ 1252 __bpf_kfunc s32 scx_bpf_pick_idle_cpu(const struct cpumask *cpus_allowed, 1253 u64 flags) 1254 { 1255 struct scx_sched *sch; 1256 1257 guard(rcu)(); 1258 1259 sch = rcu_dereference(scx_root); 1260 if (unlikely(!sch)) 1261 return -ENODEV; 1262 1263 if (static_branch_maybe(CONFIG_NUMA, &scx_builtin_idle_per_node)) { 1264 scx_error(sch, "per-node idle tracking is enabled"); 1265 return -EBUSY; 1266 } 1267 1268 if (!check_builtin_idle_enabled(sch)) 1269 return -EBUSY; 1270 1271 return scx_pick_idle_cpu(cpus_allowed, NUMA_NO_NODE, flags); 1272 } 1273 1274 /** 1275 * scx_bpf_pick_any_cpu_node - Pick and claim an idle cpu if available 1276 * or pick any CPU from @node 1277 * @cpus_allowed: Allowed cpumask 1278 * @node: target NUMA node 1279 * @flags: %SCX_PICK_IDLE_CPU_* flags 1280 * 1281 * Pick and claim an idle cpu in @cpus_allowed. If none is available, pick any 1282 * CPU in @cpus_allowed. Guaranteed to succeed and returns the picked idle cpu 1283 * number if @cpus_allowed is not empty. -%EBUSY is returned if @cpus_allowed is 1284 * empty. 1285 * 1286 * The search starts from @node and proceeds to other online NUMA nodes in 1287 * order of increasing distance (unless %SCX_PICK_IDLE_IN_NODE is specified, 1288 * in which case the search is limited to the target @node, regardless of 1289 * the CPU idle state). 1290 * 1291 * If ops.update_idle() is implemented and %SCX_OPS_KEEP_BUILTIN_IDLE is not 1292 * set, this function can't tell which CPUs are idle and will always pick any 1293 * CPU. 1294 */ 1295 __bpf_kfunc s32 scx_bpf_pick_any_cpu_node(const struct cpumask *cpus_allowed, 1296 int node, u64 flags) 1297 { 1298 struct scx_sched *sch; 1299 s32 cpu; 1300 1301 guard(rcu)(); 1302 1303 sch = rcu_dereference(scx_root); 1304 if (unlikely(!sch)) 1305 return -ENODEV; 1306 1307 node = validate_node(sch, node); 1308 if (node < 0) 1309 return node; 1310 1311 cpu = scx_pick_idle_cpu(cpus_allowed, node, flags); 1312 if (cpu >= 0) 1313 return cpu; 1314 1315 if (flags & SCX_PICK_IDLE_IN_NODE) 1316 cpu = cpumask_any_and_distribute(cpumask_of_node(node), cpus_allowed); 1317 else 1318 cpu = cpumask_any_distribute(cpus_allowed); 1319 if (cpu < nr_cpu_ids) 1320 return cpu; 1321 else 1322 return -EBUSY; 1323 } 1324 1325 /** 1326 * scx_bpf_pick_any_cpu - Pick and claim an idle cpu if available or pick any CPU 1327 * @cpus_allowed: Allowed cpumask 1328 * @flags: %SCX_PICK_IDLE_CPU_* flags 1329 * 1330 * Pick and claim an idle cpu in @cpus_allowed. If none is available, pick any 1331 * CPU in @cpus_allowed. Guaranteed to succeed and returns the picked idle cpu 1332 * number if @cpus_allowed is not empty. -%EBUSY is returned if @cpus_allowed is 1333 * empty. 1334 * 1335 * If ops.update_idle() is implemented and %SCX_OPS_KEEP_BUILTIN_IDLE is not 1336 * set, this function can't tell which CPUs are idle and will always pick any 1337 * CPU. 1338 * 1339 * Always returns an error if %SCX_OPS_BUILTIN_IDLE_PER_NODE is set, use 1340 * scx_bpf_pick_any_cpu_node() instead. 1341 */ 1342 __bpf_kfunc s32 scx_bpf_pick_any_cpu(const struct cpumask *cpus_allowed, 1343 u64 flags) 1344 { 1345 struct scx_sched *sch; 1346 s32 cpu; 1347 1348 guard(rcu)(); 1349 1350 sch = rcu_dereference(scx_root); 1351 if (unlikely(!sch)) 1352 return -ENODEV; 1353 1354 if (static_branch_maybe(CONFIG_NUMA, &scx_builtin_idle_per_node)) { 1355 scx_error(sch, "per-node idle tracking is enabled"); 1356 return -EBUSY; 1357 } 1358 1359 if (static_branch_likely(&scx_builtin_idle_enabled)) { 1360 cpu = scx_pick_idle_cpu(cpus_allowed, NUMA_NO_NODE, flags); 1361 if (cpu >= 0) 1362 return cpu; 1363 } 1364 1365 cpu = cpumask_any_distribute(cpus_allowed); 1366 if (cpu < nr_cpu_ids) 1367 return cpu; 1368 else 1369 return -EBUSY; 1370 } 1371 1372 __bpf_kfunc_end_defs(); 1373 1374 BTF_KFUNCS_START(scx_kfunc_ids_idle) 1375 BTF_ID_FLAGS(func, scx_bpf_cpu_node) 1376 BTF_ID_FLAGS(func, scx_bpf_get_idle_cpumask_node, KF_ACQUIRE) 1377 BTF_ID_FLAGS(func, scx_bpf_get_idle_cpumask, KF_ACQUIRE) 1378 BTF_ID_FLAGS(func, scx_bpf_get_idle_smtmask_node, KF_ACQUIRE) 1379 BTF_ID_FLAGS(func, scx_bpf_get_idle_smtmask, KF_ACQUIRE) 1380 BTF_ID_FLAGS(func, scx_bpf_put_idle_cpumask, KF_RELEASE) 1381 BTF_ID_FLAGS(func, scx_bpf_test_and_clear_cpu_idle) 1382 BTF_ID_FLAGS(func, scx_bpf_pick_idle_cpu_node, KF_RCU) 1383 BTF_ID_FLAGS(func, scx_bpf_pick_idle_cpu, KF_RCU) 1384 BTF_ID_FLAGS(func, scx_bpf_pick_any_cpu_node, KF_RCU) 1385 BTF_ID_FLAGS(func, scx_bpf_pick_any_cpu, KF_RCU) 1386 BTF_ID_FLAGS(func, scx_bpf_select_cpu_and, KF_RCU) 1387 BTF_ID_FLAGS(func, scx_bpf_select_cpu_dfl, KF_RCU) 1388 BTF_KFUNCS_END(scx_kfunc_ids_idle) 1389 1390 static const struct btf_kfunc_id_set scx_kfunc_set_idle = { 1391 .owner = THIS_MODULE, 1392 .set = &scx_kfunc_ids_idle, 1393 }; 1394 1395 int scx_idle_init(void) 1396 { 1397 int ret; 1398 1399 ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &scx_kfunc_set_idle) || 1400 register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &scx_kfunc_set_idle) || 1401 register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &scx_kfunc_set_idle); 1402 1403 return ret; 1404 } 1405