1 // SPDX-License-Identifier: GPL-2.0-only
33  * Any bug related to task migration is likely to be timing-dependent; perform
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()
108 		 * Wait 1-10us before proceeding to the next iteration and more  in migration_worker()
118 		 *     the guest, the guest will trigger a IO/MMIO exit all the  in migration_worker()
120 		 *     the generic "exit to userspace" logic, not by KVM.  The  in migration_worker()
121 		 *     exit to userspace is necessary to give the test a chance  in migration_worker()
125 		 *     to trigger an exit that is handled by KVM, but any such  in migration_worker()
126 		 *     exit requires architecture specific code.  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()
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()
142 		 * run with a range of delays at 1us intervals from 1us to 10us  in migration_worker()
147 		 * The original bug can reproduce with a delay up to ~500us on  in migration_worker()
148 		 * x86-64, but starts to require more iterations to reproduce  in migration_worker()
149 		 * as the delay creeps above ~10us, and the average runtime of  in migration_worker()
151 		 * at 10us to keep test runtime reasonable while minimizing  in migration_worker()
154 		 * The lower bound for reproducing the bug is likely below 1us,  in migration_worker()
155 		 * e.g. failures occur on x86-64 with nanosleep(0), but at that  in migration_worker()
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()
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()
203 	exit(0);  in help()
208 	int r, i, snapshot, opt, fd = -1, latency = -1;  in main()  local
214 	while ((opt = getopt(argc, argv, "hl:u")) != -1) {  in main()
219 			latency = atoi_paranoid(optarg);  in main()
248 	if (latency >= 0) {  in main()
251 		 * open, i.e. it allows userspace to provide guaranteed latency  in main()
258 		r = write(fd, &latency, 4);  in main()
271 		 * count is odd (migration in-progress).  in main()
276 			 * i.e. if a migration is in-progress.  in main()
304 	 * conservative ratio on x86-64, which can do _more_ KVM_RUNs than  in main()
305 	 * migrations given the 1us+ delay in the migration task.  in main()
308 	 * on systems with large low power mode wakeup latency, it may happen  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()