Messages in this thread | ![/](/images/icornerl.gif) | | Subject | Re: [PATCH] watchdog: nohz: don't run watchdog on nohz_full cores | From | Mike Galbraith <> | Date | Tue, 31 Mar 2015 04:04:35 +0200 |
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On Mon, 2015-03-30 at 15:12 -0400, Don Zickus wrote: > On Mon, Mar 30, 2015 at 02:51:05PM -0400, cmetcalf@ezchip.com wrote: > > From: Chris Metcalf <cmetcalf@ezchip.com> > > > > Running watchdog can be a helpful debugging feature on regular > > cores, but it's incompatible with nohz_full, since it forces > > regular scheduling events. Accordingly, just exit out immediately > > from any nohz_full core. > > > > An alternate approach would be to add a flags field or function to > > smp_hotplug_thread to control on which cores the percpu threads > > are created, but it wasn't clear that much mechanism was useful. > > Hi Chris, > > It seems like the correct solution would be to hook into the idle_loop > somehow. If the cpu is idle, then it seems unlikely that a lockup could > occur. > > My fear with this apporach is a lockup would occur on the nohz cpu and it > would go undetected because that cpu is disabled. Further no printk is > thrown out to even indicate a cpu is disabled making it more difficult to > debug.
Hm, I don't see why this is needed, for debugging/testing you turn it on, when you set up for critical operation, you turn it off.
A bigger deal is the clocksource watchdog methinks. Measurement inspired me to make it dead yesterday.
-Mike
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