1 // SPDX-License-Identifier: GPL-2.0-only
33  * Any bug related to task migration is likely to be timing-dependent; perform
51 static int next_cpu(int cpu)  in next_cpu()  argument
54 	 * Advance to the next CPU, skipping those that weren't in the original  in next_cpu()
58 	 * burn a lot cycles and the test will take longer than normal to  in next_cpu()
62 		cpu++;  in next_cpu()
63 		if (cpu > max_cpu) {  in next_cpu()
64 			cpu = min_cpu;  in next_cpu()
65 			TEST_ASSERT(CPU_ISSET(cpu, &possible_mask),  in next_cpu()
66 				    "Min CPU = %d must always be usable", cpu);  in next_cpu()
69 	} while (!CPU_ISSET(cpu, &possible_mask));  in next_cpu()
71 	return cpu;  in next_cpu()
78 	int r, i, cpu;  in migration_worker()  local
82 	for (i = 0, cpu = min_cpu; i < NR_TASK_MIGRATIONS; i++, cpu = next_cpu(cpu)) {  in migration_worker()
83 		CPU_SET(cpu, &allowed_mask);  in migration_worker()
88 		 * CPU ID reads.  An odd sequence count indicates a migration  in migration_worker()
89 		 * is in-progress, while a completely different count indicates  in migration_worker()
96 		 * stable, i.e. while changing affinity is in-progress.  in migration_worker()
105 		CPU_CLR(cpu, &allowed_mask);  in migration_worker()
108 		 * Wait 1-10us before proceeding to the next iteration and more  in migration_worker()
121 		 *     exit to userspace is necessary to give the test a chance  in migration_worker()
122 		 *     to check the rseq CPU ID (see #2).  in migration_worker()
128 		 *  2. To let ioctl(KVM_RUN) make its way back to the test  in migration_worker()
129 		 *     before the next round of migration.  The test's check on  in migration_worker()
130 		 *     the rseq CPU ID must wait for migration to complete in  in migration_worker()
135 		 *  3. To ensure the read-side makes efficient forward progress,  in migration_worker()
136 		 *     e.g. if getcpu() involves a syscall. Stalling the read-side  in migration_worker()
137 		 *     means the test will spend more time waiting for getcpu()  in migration_worker()
138 		 *     to stabilize and less time trying to hit the timing-dependent  in migration_worker()
141 		 * Because any bug in this area is likely to be timing-dependent,  in migration_worker()
143 		 * as a best effort to avoid tuning the test to the point where  in migration_worker()
148 		 * x86-64, but starts to require more iterations to reproduce  in migration_worker()
151 		 * at 10us to keep test runtime reasonable while minimizing  in migration_worker()
155 		 * e.g. failures occur on x86-64 with nanosleep(0), but at that  in migration_worker()
173 	 * CPU_SET doesn't provide a FOR_EACH helper, get the min/max CPU that  in calc_min_max_cpu()
179 	min_cpu = -1;  in calc_min_max_cpu()
180 	max_cpu = -1;  in calc_min_max_cpu()
186 		if (min_cpu == -1)  in calc_min_max_cpu()
193 		       "Only one usable CPU, task migration not possible");  in calc_min_max_cpu()
199 	printf("usage: %s [-h] [-u] [-l latency]\n", name);  in help()
200 	printf(" -u: Don't sanity check the number of successful KVM_RUNs\n");  in help()
201 	printf(" -l: Set /dev/cpu_dma_latency to suppress deep sleep states\n");  in help()
208 	int r, i, snapshot, opt, fd = -1, latency = -1;  in main()
212 	u32 cpu, rseq_cpu;  in main()  local
214 	while ((opt = getopt(argc, argv, "hl:u")) != -1) {  in main()
241 	 * CPU affinity.  in main()
252 		 * while running a workload.  Keep the file open until the test  in main()
268 		 * Verify rseq's CPU matches sched's CPU.  Ensure migration  in main()
271 		 * count is odd (migration in-progress).  in main()
276 			 * i.e. if a migration is in-progress.  in main()
286 			r = sys_getcpu(&cpu, NULL);  in main()
293 		TEST_ASSERT(rseq_cpu == cpu,  in main()
294 			    "rseq CPU = %d, sched CPU = %d", rseq_cpu, cpu);  in main()
301 	 * Sanity check that the test was able to enter the guest a reasonable  in main()
304 	 * conservative ratio on x86-64, which can do _more_ KVM_RUNs than  in main()
309 	 * quite often that the scheduler is not able to wake up the target CPU  in main()
310 	 * before the vCPU thread is scheduled to another CPU.  in main()
314 		    "  Try disabling deep sleep states to reduce CPU wakeup latency,\n"  in main()
315 		    "  e.g. via cpuidle.off=1 or via -l <latency>, or run with -u to\n"  in main()