On Thu, Aug 05, 2021 at 01:39:40PM +0800, Chao Gao wrote: > [snip] > >> This patch works well; no false-positive (marking TSC unstable) in a > >> 10hr stress test. > > > >Very good, thank you! May I add your Tested-by? > > sure. > Tested-by: Chao Gao <chao.gao@xxxxxxxxx> Very good, thank you! I will apply this on the next rebase. > >I expect that I will need to modify the patch a bit more to check for > >a system where it is -never- able to get a good fine-grained read from > >the clock. > > Agreed. > > >And it might be that your test run ended up in that state. > > Not that case judging from kernel logs. Coarse-grained check happened 6475 > times in 43k seconds (by grep "coarse-grained skew check" in kernel logs). > So, still many checks were fine-grained. Whew! ;-) So about once per 13 clocksource watchdog checks. To Andi's point, do you have enough information in your console log to work out the longest run of course-grained clocksource checks? > >My current thought is that if more than (say) 100 consecutive attempts > >to read the clocksource get hit with excessive delays, it is time to at > >least do a WARN_ON(), and maybe also time to disable the clocksource > >due to skew. The reason is that if reading the clocksource -always- > >sees excessive delays, perhaps the clock driver or hardware is to blame. > > > >Thoughts? > > It makes sense to me. Sounds good! Thanx, Paul
