Messages in this thread | | | Date | Wed, 29 Apr 2015 15:26:29 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH v9 2/3] watchdog: add watchdog_cpumask sysctl to assist nohz |
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On Fri, 17 Apr 2015 14:37:17 -0400 Chris Metcalf <cmetcalf@ezchip.com> wrote:
> Change the default behavior of watchdog so it only runs on the > housekeeping cores when nohz_full is enabled at build and boot time. > Allow modifying the set of cores the watchdog is currently running > on with a new kernel.watchdog_cpumask sysctl. > > If we allowed the watchdog to run on nohz_full cores, the timer > interrupts and scheduler work would prevent the desired tickless > operation on those cores. But if we disable the watchdog globally, > then the housekeeping cores can't benefit from the watchdog > functionality. So we allow disabling it only on some cores. > See Documentation/lockup-watchdogs.txt for more information.
Could you please expand on the patch motivation? "would prevent the desired tickless operation on those cores" is quite vague.
Exactly what userspace-visible problem is the current implementation causing and how does the patchset improve things?
If any of this is quantifiable (wakeups/sec, joules/hour etc) then some attempt to perform those measurements would also be useful.
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