On Thu, Aug 11, 2016 at 10:40:02AM +0200, Peter Zijlstra wrote: > On Thu, Aug 11, 2016 at 12:16:58AM +0200, Frederic Weisbecker wrote: > > I had similar issues, this seems to happen when the tsc is considered not reliable > > (which doesn't necessarily mean unstable. I think it has to do with some x86 CPU feature > > flag). > > Right, as per the other email, in general we cannot know/assume the TSC > to be working as intended :/ Yeah, I remember you explained me that a little while ago. > > > IIRC, this _has_ to execute on all online CPUs because every TSCs of running CPUs > > are concerned. > > With modern Intel we could run it on one CPU per package I think, but at > the same time, too much in NOHZ_FULL assumes the TSC is indeed sane so > it doesn't make sense to me to keep the watchdog running, when it > triggers it would also have to kill all NOHZ_FULL stuff, which would > probably bring the entire machine down.. > > Arguably we should issue a boot time warning if NOHZ_FULL is configured > and the TSC watchdog is running. That's a very good idea! We do that when tsc is unstable but indeed we can't seriously run NOHZ_FULL on a non-reliable tsc. I'll take care of that warning. > > > I personally override that with passing the tsc=reliable kernel > > parameter. Of course use it at your own risk. > > Yes, that is (sadly) our only option. Manually assert our hardware is > solid under the intended workload and then manually disabling the > watchdog. Right, I'll tell about that in the warning. Thanks for those details! -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
