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1 .. SPDX-License-Identifier: GPL-2.0
44 performance point required by its display pipeline to ensure no frame is
57 foreground, top-app, etc. Util clamp can be used to constrain how much
60 the ones belonging to the currently active app (top-app group). Beside this
65 1. The big cores are free to run top-app tasks immediately. top-app
106 Note that by design RT tasks don't have per-task PELT signal and must always
114 See :ref:`section 3.4 <uclamp-default-values>` for default values and
115 :ref:`3.4.1 <sched-util-clamp-min-rt-default>` on how to change RT tasks
150 task on the rq to only a subset of tasks on the top-most bucket.
156 As tasks are enqueued and dequeued, we keep track of the current effective
157 uclamp value of the rq. See :ref:`section 2.1 <uclamp-buckets>` for details on
167 When a task wakes up, the scheduler will look at the current effective uclamp
173 at the current effective uclamp value of the rq which is influenced by the set
182 .. _uclamp-buckets:
185 ------------
195 +-----------+-----------+-----------+---- ----+-----------+
197 +-----------+-----------+-----------+---- ----+-----------+
199 +- p0 +- p3 +- p4
201 +- p1 +- p5
203 +- p2
234 p->uclamp[UCLAMP_MIN] = 300
235 p->uclamp[UCLAMP_MAX] = 1024
241 The rq then keeps track of its current effective uclamp value for each
249 rq->uclamp[UCLAMP_MIN] = max(rq->uclamp[UCLAMP_MIN], p->uclamp[UCLAMP_MIN])
257 rq->uclamp[UCLAMP_MIN] = search_top_bucket_for_highest_value()
261 See :ref:`section 3.4 <uclamp-default-values>` for details on default values.
265 --------------------
279 p0->uclamp[UCLAMP_MIN] = 300
280 p0->uclamp[UCLAMP_MAX] = 900
282 p1->uclamp[UCLAMP_MIN] = 500
283 p1->uclamp[UCLAMP_MAX] = 500
290 rq->uclamp[UCLAMP_MIN] = max(300, 500) = 500
291 rq->uclamp[UCLAMP_MAX] = max(900, 500) = 900
293 As we shall see in :ref:`section 5.1 <uclamp-capping-fail>`, this max
298 -----------------------------
311 :ref:`Section 3 <uclamp-interfaces>` discusses the interfaces and will expand
328 ----------
335 .. _uclamp-interfaces:
341 -----------------------
354 attr->sched_util_min = 40% * 1024;
355 attr->sched_util_max = 80% * 1024;
362 The special value -1 is used to reset the uclamp settings to the system
365 Note that resetting the uclamp value to system default using -1 is not the same
372 ---------------------
382 * cpu.uclamp.min is a protection as described in :ref:`section 3-3 of cgroup
383 v2 documentation <cgroupv2-protections-distributor>`.
391 * cpu.uclamp.max is a limit as described in :ref:`section 3-2 of cgroup v2
392 documentation <cgroupv2-limits-distributor>`.
404 p0->uclamp[UCLAMP_MIN] = // system default;
405 p0->uclamp[UCLAMP_MAX] = // system default;
407 p1->uclamp[UCLAMP_MIN] = 40% * 1024;
408 p1->uclamp[UCLAMP_MAX] = 50% * 1024;
410 cgroup0->cpu.uclamp.min = 20% * 1024;
411 cgroup0->cpu.uclamp.max = 60% * 1024;
413 cgroup1->cpu.uclamp.min = 60% * 1024;
414 cgroup1->cpu.uclamp.max = 100% * 1024;
420 p0->uclamp[UCLAMP_MIN] = cgroup0->cpu.uclamp.min = 20% * 1024;
421 p0->uclamp[UCLAMP_MAX] = cgroup0->cpu.uclamp.max = 60% * 1024;
423 p1->uclamp[UCLAMP_MIN] = 40% * 1024; // intact
424 p1->uclamp[UCLAMP_MAX] = 50% * 1024; // intact
430 p0->uclamp[UCLAMP_MIN] = cgroup1->cpu.uclamp.min = 60% * 1024;
431 p0->uclamp[UCLAMP_MAX] = cgroup1->cpu.uclamp.max = 100% * 1024;
433 p1->uclamp[UCLAMP_MIN] = cgroup1->cpu.uclamp.min = 60% * 1024;
434 p1->uclamp[UCLAMP_MAX] = 50% * 1024; // intact
440 ---------------------
443 --------------------------
445 System wide limit of allowed UCLAMP_MIN range. By default it is set to 1024,
451 they won't be satisfied until it is more than p->uclamp[UCLAMP_MIN].
456 --------------------------
458 System wide limit of allowed UCLAMP_MAX range. By default it is set to 1024,
462 [0:512]. This means is that no task can run above 512, which implies that all
467 For example, it can be handy to limit performance when running low on battery
468 or when the system wants to limit access to more energy hungry performance
472 won't be satisfied until it is more than p->uclamp[UCLAMP_MAX].
476 .. _uclamp-default-values:
479 -------------------
485 p_fair->uclamp[UCLAMP_MIN] = 0
486 p_fair->uclamp[UCLAMP_MAX] = 1024
489 changed at boot or runtime. No argument was made yet as to why we should
496 p_rt->uclamp[UCLAMP_MIN] = 1024
497 p_rt->uclamp[UCLAMP_MAX] = 1024
505 .. _sched-util-clamp-min-rt-default:
508 -------------------------------------
526 management. At the scheduler level there is no info required to make the best
543 4.1. Boost important and DVFS-latency-sensitive tasks
544 -----------------------------------------------------
564 -------------------------
571 -------------------
573 sched_util_clamp_max system wide interface can be used to limit all tasks from
581 4.4. Per-app performance restriction
582 ------------------------------------
586 limit it from draining system power at the cost of reduced performance for
597 .. _uclamp-capping-fail:
600 ---------------------------------------------------------------------
606 p0->uclamp[UCLAMP_MAX] = 512
612 p1->uclamp[UCLAMP_MAX] = 1024
619 rq->uclamp[UCLAMP_MAX] = max(512, 1024) = 1024
630 ------------------------------------------------
634 increase will be prevented which can lead to no idle time in some
635 circumstances. When there's no idle time, a task will stuck in a busy loop,
645 p0->util_avg = 300
646 p0->uclamp[UCLAMP_MAX] = 0
655 rq->uclamp[UCLAMP_MAX] = 0
665 long as there's idle time, p->util_avg updates will be off by a some margin,
670 p0->util_avg = 300 + small_error
678 which is higher than 1024 and indicates that the CPU has no idle time. When
683 p0->util_avg = 1024
689 p1->util_avg = 200
690 p1->uclamp[UCLAMP_MAX] = 1024
694 severely, then the rq->util_avg will be:
698 p0->util_avg = 1024
699 p1->util_avg = 200
701 rq->util_avg = 1024
702 rq->uclamp[UCLAMP_MAX] = 1024
708 p0->util_avg = 300
709 p1->util_avg = 200
711 rq->util_avg = 500
716 -----------------------------------
720 1. Hardware takes non-zero time to respond to any frequency change
722 2. Non fast-switch systems require a worker deadline thread to wake up
733 prevalent as we no longer gradually ramp up or down. We could easily be