https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=198149
--- Comment #14 from John Baldwin <j...@freebsd.org> --- This survived an overnight run with pmcstat still getting samples this morning. I added debugging to print a message each time one of these fixes was applied (and in the case of the first patch, I outputted the raw value of the PMC). Both of these conditions fired fairly consistently during the test (once every few seconds or so). In addition, when I had run with just the first patch, I had seen raw PMC counter values that in my debug messages that could be a bit large, for example: CPU 1: counter overflowed: 87516 CPU 1: counter overflowed: 22 CPU 12: counter overflowed: 2 CPU 1: counter overflowed: 2 CPU 1: counter overflowed: 13629 CPU 1: counter overflowed: 2 CPU 1: counter overflowed: 2 With both patches applied I do not see "large" values, only small ones: CPU 5: fixing zero PMC CPU 1: counter overflowed: 20 CPU 1: fixing zero PMC CPU 1: counter overflowed: 2 CPU 1: fixing zero PMC CPU 1: fixing zero PMC CPU 15: fixing zero PMC CPU 1: fixing zero PMC CPU 1: counter overflowed: 4 CPU 1: counter overflowed: 2 CPU 1: counter overflowed: 2 CPU 1: fixing zero PMC CPU 1: counter overflowed: 2 CPU 1: fixing zero PMC CPU 1: counter overflowed: 2 CPU 8: fixing zero PMC CPU 1: counter overflowed: 2 CPU 1: counter overflowed: 2 CPU 1: counter overflowed: 2 CPU 2: counter overflowed: 2 CPU 9: counter overflowed: 2 CPU 3: fixing zero PMC CPU 8: fixing zero PMC CPU 1: counter overflowed: 22 CPU 1: fixing zero PMC CPU 1: fixing zero PMC CPU 1: counter overflowed: 2 CPU 1: counter overflowed: 27 CPU 1: counter overflowed: 5 CPU 1: fixing zero PMC ..... I had wondered if the second bug (writing a PMC value of zero) could have been the source of the second bug (you can see how it would easily trigger it: if you write a PMC of zero and the event happens 2 times before your next context switch you would have a raw value of "2" when you switched out). However, whilt it seems to have fixed some of them (the "large" ones) it does not seem to have fixed all of them. I definitely think the second fix is probably legit (and has been present since sampling was added to PMC). I think the first change is also technically correct, but I'm not sure why we are seeing those values. -- You are receiving this mail because: You are the assignee for the bug. _______________________________________________ freebsd-bugs@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-bugs To unsubscribe, send any mail to "freebsd-bugs-unsubscr...@freebsd.org"
