On 1 December 2017 at 07:15, Robert Elliott (Persistent Memory) <elliott@xxxxxxx> wrote: > While discussing NUMA, I'll mention something else I saw in Windows > while fixing the thread affinities there. > > At startup, fio spawns threads on all CPUs to measure the clocks > (fio_monotonic_clocktest). If you've constrained the CPU affinity > outside fio, some of those will fail. In Windows, something like > START /AFFINITY 0x55555555 fio ... > can cause half of the clock threads to fail. This is very weird and doesn't make any sense (but I believe you): if you have multiple threads crammed on to the same CPUs the TSC no longer looks like it monotonically increases? Surely it should be MORE likely to increase because a thread is likely to be on the same CPU as another and can't actually be running at the same time as the other? Something suspicious is going on - to this day I'm still unsure as to why https://github.com/sitsofe/fio/commit/1a7a1fd98ad749768212f49f5ba3e9a1392c4263 would sometimes fail on Windows (but seemingly not on Linux)... -- Sitsofe | http://sucs.org/~sits/ -- To unsubscribe from this list: send the line "unsubscribe fio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
