Messages in this thread | | | Date | Mon, 13 Apr 2015 11:48:16 -0400 | From | Chris Metcalf <> | Subject | Re: [PATCH v7 1/3] smpboot: allow excluding cpus from the smpboot threads |
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On 04/10/2015 05:11 PM, Andrew Morton wrote: > On Fri, 10 Apr 2015 16:48:18 -0400 Chris Metcalf <cmetcalf@ezchip.com> wrote: > >> This change allows some cores to be excluded from running the >> smp_hotplug_thread tasks. The motivating example for this is >> the watchdog threads, which by default we don't want to run >> on any enabled nohz_full cores. > Why not?
Thanks for the feedback. It's easy to assume everyone knows everything about what's being done in the kernel :-)
I'll add some more descriptive language around what the point of nohz_full is, and why the watchdog interferes with it, in v8.
> > I can guess, but I'd rather not guess. Please fully explain the > end-user value of this change. Providing a benefit to users is the > whole point of the patchset, but the above assertion is the only > description we have. > > This info should be in Documentation/lockup-watchdogs.txt and/or > Documentation/sysctl/kernel.txt as well as the changelogs, so users > have an answer to "why the heck should I enable this". > > Please also describe the downside of the change. I assume this is > "lockups will go undetected on some CPUs"? Let's expand on this so we > can understand where the best tradeoff point lies. > > If people are experiencing <whatever this problem is> then they can > disable the watchdog altogether. What value is there in this partial > disabling? Why is it worth doing this? >
-- Chris Metcalf, EZChip Semiconductor http://www.ezchip.com
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