On Wed 2018-07-18 19:49:10, Andy Shevchenko wrote: > On Tue, Jul 17, 2018 at 3:59 AM, Dmitry Safonov <dima@xxxxxxxxxx> wrote: > > I would be glad if someone helps/bothers to review the change :C > > > > Perhaps Petr and / or Steven can help you. > > Thanks, > > Dmitry > > > > On Tue, 2018-07-03 at 23:56 +0100, Dmitry Safonov wrote: > >> Currently ratelimit_state is protected with spin_lock. If the .lock > >> is > >> taken at the moment of ___ratelimit() call, the message is suppressed > >> to > >> make ratelimiting robust. > >> > >> That results in the following issue issue: > >> CPU0 CPU1 > >> ------------------ ------------------ > >> printk_ratelimit() printk_ratelimit() > >> | | > >> try_spin_lock() try_spin_lock() > >> | | > >> time_is_before_jiffies() return 0; // suppress > >> > >> So, concurrent call of ___ratelimit() results in silently suppressing > >> one of the messages, regardless if the limit is reached or not. > >> And rc->missed is not increased in such case so the issue is covered > >> from user. > >> > >> Convert ratelimiting to use atomic counters and drop spin_lock. > >> > >> Note: That might be unexpected, but with the first interval of > >> messages > >> storm one can print up to burst*2 messages. So, it doesn't guarantee > >> that in *any* interval amount of messages is lesser than burst. > >> But, that differs lightly from previous behavior where one can start > >> burst=5 interval and print 4 messages on the last milliseconds of > >> interval + new 5 messages from new interval (totally 9 messages in > >> lesser than interval value): > >> > >> msg0 msg1-msg4 msg0-msg4 > >> | | | > >> | | | > >> |--o---------------------o-|-----o--------------------|--> (t) > >> <-------> > >> Lesser than burst > >> I am a bit confused. Does this patch fix two problems? + Lost rc->missed update when try_spin_lock() fails + printing up to burst*2 messages in a give interval It would make the review much easier if you split it into more patches and fix the problems separately. Otherwise, it looks promissing... Best Regards, Petr PS: I have vacation the following two weeks. Anyway, please, CC me if you send any new version. Best Regards, Petr _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
