-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 08/12/2014 03:12 PM, Oleg Nesterov wrote:
> Afaics, the problem is that a single thread can observe the > decreasing (say) sum_exec_runtime if it calls do_sys_times() twice > without the lock. > > This is because it can account the exiting sub-thread twice if it > races with __exit_signal() which increments sig->sum_sched_runtime, > but this exiting thread can still be visible to > thread_group_cputime(). > > IOW, it is not actually about decreasing, the problem is that the > lockless thread_group_cputime() can return the wrong result, and > the next ys_times() can show the right value. You are right, changing the test case to call times() many times in a row in each thread can result in the wrong value being returned. Not entirely sure what I can do there... Replacing the spinlock with a seqlock, and taking it for write in most places is pretty gross, and may lead to other issues like reader livelock when there is a lot of write activity. Having a seqlock just for the stats? Not sure the calls to times() are a big enough issue for most workloads to justify that... Any other ideas? - -- All rights reversed -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQEcBAEBAgAGBQJT6pTdAAoJEM553pKExN6DMrIIAKFFHD8luyqgVUAm0jbV8JHm O5PD81kot95POV7ZAl6crKmPi0OoeSdZIzcmuLFIvRJWqrbgWY6h4rQH9va5B830 F7TC2PRzWwUVwcuEoaUkuZMbUWkWqzUwXcwwFl1blYmkVJVRF27VcUB4S0jia1eq l2TlQyC1HgXa3E7rbQ6vuKsOq50jB08MWwxEfhAEMNvndhos/fvZlsxL39UO3/X7 AVk+V/leE5tfAfyr6uPrWDR7/u9sJkqmi/dGJ/xjfWNU2swEPvMXk6UhspSIY+mg KAMa+JWTPANeUSRM9HRA9YUpo0rqvy0Azmg84tIYr4nXsIyvzHuRgCUNQkOmEDQ= =5ap3 -----END PGP SIGNATURE----- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
