On 12/03/2017 02:35 AM, Sitsofe Wheeler wrote: > 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? The threads fail to start, it's not a TSC failure. I'm guessing it's because fio gets limited to a subset of the available CPUs, and that causes fio to fail doing the clock check when fio_setaffinity() in clock_thread_fn() fails. -- Jens Axboe -- 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
