1 // SPDX-License-Identifier: GPL-2.0-only
26  * Any bug related to task migration is likely to be timing-dependent; perform
44 static int next_cpu(int cpu)  in next_cpu()  argument
47 	 * Advance to the next CPU, skipping those that weren't in the original  in next_cpu()
51 	 * burn a lot cycles and the test will take longer than normal to  in next_cpu()
55 		cpu++;  in next_cpu()
56 		if (cpu > max_cpu) {  in next_cpu()
57 			cpu = min_cpu;  in next_cpu()
58 			TEST_ASSERT(CPU_ISSET(cpu, &possible_mask),  in next_cpu()
59 				    "Min CPU = %d must always be usable", cpu);  in next_cpu()
62 	} while (!CPU_ISSET(cpu, &possible_mask));  in next_cpu()
64 	return cpu;  in next_cpu()
71 	int r, i, cpu;  in migration_worker()  local
75 	for (i = 0, cpu = min_cpu; i < NR_TASK_MIGRATIONS; i++, cpu = next_cpu(cpu)) {  in migration_worker()
76 		CPU_SET(cpu, &allowed_mask);  in migration_worker()
81 		 * CPU ID reads.  An odd sequence count indicates a migration  in migration_worker()
82 		 * is in-progress, while a completely different count indicates  in migration_worker()
89 		 * stable, i.e. while changing affinity is in-progress.  in migration_worker()
98 		CPU_CLR(cpu, &allowed_mask);  in migration_worker()
101 		 * Wait 1-10us before proceeding to the next iteration and more  in migration_worker()
114 		 *     exit to userspace is necessary to give the test a chance  in migration_worker()
115 		 *     to check the rseq CPU ID (see #2).  in migration_worker()
121 		 *  2. To let ioctl(KVM_RUN) make its way back to the test  in migration_worker()
122 		 *     before the next round of migration.  The test's check on  in migration_worker()
123 		 *     the rseq CPU ID must wait for migration to complete in  in migration_worker()
128 		 *  3. To ensure the read-side makes efficient forward progress,  in migration_worker()
129 		 *     e.g. if getcpu() involves a syscall. Stalling the read-side  in migration_worker()
130 		 *     means the test will spend more time waiting for getcpu()  in migration_worker()
131 		 *     to stabilize and less time trying to hit the timing-dependent  in migration_worker()
134 		 * Because any bug in this area is likely to be timing-dependent,  in migration_worker()
136 		 * as a best effort to avoid tuning the test to the point where  in migration_worker()
141 		 * x86-64, but starts to require more iterations to reproduce  in migration_worker()
144 		 * at 10us to keep test runtime reasonable while minimizing  in migration_worker()
148 		 * e.g. failures occur on x86-64 with nanosleep(0), but at that  in migration_worker()
166 	 * CPU_SET doesn't provide a FOR_EACH helper, get the min/max CPU that  in calc_min_max_cpu()
172 	min_cpu = -1;  in calc_min_max_cpu()
173 	max_cpu = -1;  in calc_min_max_cpu()
179 		if (min_cpu == -1)  in calc_min_max_cpu()
186 		       "Only one usable CPU, task migration not possible");  in calc_min_max_cpu()
194 	u32 cpu, rseq_cpu;  in main()  local
209 	 * CPU affinity.  in main()
222 		 * Verify rseq's CPU matches sched's CPU.  Ensure migration  in main()
225 		 * count is odd (migration in-progress).  in main()
230 			 * i.e. if a migration is in-progress.  in main()
240 			r = sys_getcpu(&cpu, NULL);  in main()
247 		TEST_ASSERT(rseq_cpu == cpu,  in main()
248 			    "rseq CPU = %d, sched CPU = %d", rseq_cpu, cpu);  in main()
252 	 * Sanity check that the test was able to enter the guest a reasonable  in main()
255 	 * conservative ratio on x86-64, which can do _more_ KVM_RUNs than  in main()