> Thinking back on this, you'll want a program that does the following > on a system with N CPUs: > > - Phase 1: run one thread per cpu, pinned on each cpu. Print the > mm_cid from each thread with the cpu number every second or so. > > - Exit all threads except the main thread, join them from the main > thread, > > - Phase 2: the program is now single-threaded. We'd expect the > mm_cid value to converge towards 0 as the periodic task clears > unused CIDs. > > So I think in phase 2 we can have an actual automated test: If after > an order of magnitude more time than the 100ms delay between periodic > tasks we still observe mm_cid > 0 in phase 2, then something is > wrong. Been thinking about this and came up with a simple draft, I'll probably send it as a separate patch. Doing this can lead to false positives: the main thread may be assigned the mm_cid 0 and keep it till the end, in this scenario the other threads (CPUs) would get different mm_cids and exit, the main thread will still have 0 and pass the test regardless. I have an idea to make it a bit more robust: we can run threads as you described in phase 1, stop all but one (let's say the one running on the last core), make sure the main thread doesn't accidentally run on the same core by pinning to core 0 and wait until we see the 2 remaining threads holding 0 and 1, in any order. Besides a special case if we have only 1 available core, this should work fine, sure we could get false positives but it seems to me much less likely. Does it make sense to you? Gabriele
