On Wed, Oct 09, 2013 at 09:55:19AM -0400, Don Zickus wrote: > On Tue, Oct 08, 2013 at 07:08:11PM -0300, Marcelo Tosatti wrote: > > On Tue, Oct 08, 2013 at 09:37:05AM -0400, Don Zickus wrote: > > > On Mon, Oct 07, 2013 at 10:05:17PM -0300, Marcelo Tosatti wrote: > > > > Implement reset of kernel watchdogs at pvclock read time. This avoids > > > > adding special code to every watchdog. > > > > > > > > This is possible for watchdogs which measure time based on sched_clock() or > > > > ktime_get() variants. > > > > > > > > Suggested by Don Zickus. > > > > > > > > Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx> > > > > > > Awesome. Thanks for figuring this out Marcelo. Does that mean we can > > > revert commit 5d1c0f4a now? :-) > > > > Unfortunately no: soft lockup watchdog does not measure time based on > > sched_clock but on hrtimer interrupt count :-( > > I believe it does. See __touch_watchdog() which calls get_timestamp() --> > local_clock(). That is how it calculates the duration of the softlockup. > > Now with your patch, it just sets the timestamp to zero with > touch_softlockup_watchdog_sync(), which is fine. It will just sync up the > clock, set a new timestamp, and check again in the next hrtimer interrupt. > > So I guess I am confused what that commit does compared to this patch. > > > (see the the softlockup code in question, perhaps you can point to > > something that i'm missing). > > > > BTW, are you OK with printing additional steal time information? > > https://lkml.org/lkml/2013/6/27/755 > > Well, I thought this patch was supposed to replace that patch? Why do you > still need that patch? >From https://lkml.org/lkml/2013/7/3/675: "Agree. However, can't see how there is a way around "having custom kvm/paravirt splat all over", for watchdogs that do: 1. check for watchdog resets 2. read time via sched_clock or xtime. 3. based on 2, decide whether there has been a longer delay than acceptable. This is the case for the softlockup timer interrupt. So the splat there is necessary (otherwise any potential notification of vm-pause event noticed at 2 might be missed because its checked at 1). For watchdogs that measure time based on interrupt event (such as hung task, rcu_cpu_stall, checking for the notification at sched_clock or lower is fine)." -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
