1 // SPDX-License-Identifier: GPL-2.0-only
26  * Any bug related to task migration is likely to be timing-dependent; perform
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()
101 		 * Wait 1-10us before proceeding to the next iteration and more  in migration_worker()
102 		 * specifically, before bumping seq_cnt again.  A delay is  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()
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()
135 		 * run with a range of delays at 1us intervals from 1us to 10us  in migration_worker()
140 		 * The original bug can reproduce with a delay up to ~500us on  in migration_worker()
141 		 * x86-64, but starts to require more iterations to reproduce  in migration_worker()
142 		 * as the delay creeps above ~10us, and the average runtime of  in migration_worker()
143 		 * each iteration obviously increases as well.  Cap the delay  in migration_worker()
144 		 * at 10us to keep test runtime reasonable while minimizing  in migration_worker()
147 		 * The lower bound for reproducing the bug is likely below 1us,  in migration_worker()
148 		 * e.g. failures occur on x86-64 with nanosleep(0), but at that  in migration_worker()
149 		 * point the overhead of the syscall likely dominates the delay.  in migration_worker()
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()
225 		 * count is odd (migration in-progress).  in main()
230 			 * i.e. if a migration is in-progress.  in main()
255 	 * conservative ratio on x86-64, which can do _more_ KVM_RUNs than  in main()
256 	 * migrations given the 1us+ delay in the migration task.  in main()