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Date: Thu, 2 Apr 2015 18:48:48 +0200
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Don Zickus <dzickus@redhat.com>, Ingo Molnar <mingo@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrew Jones <drjones@redhat.com>,
        chai wen <chaiw.fnst@cn.fujitsu.com>,
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        Fabian Frederick <fabf@skynet.be>, Aaron Tomlin <atomlin@redhat.com>,
        Ben Zhang <benzh@chromium.org>, Christoph Lameter <cl@linux.com>,
        Gilad Ben-Yossef <gilad@benyossef.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] watchdog: nohz: don't run watchdog on nohz_full cores
Message-ID: <20150402164845.GD10357@lerouge>
References: <1427741465-15747-1-git-send-email-cmetcalf@ezchip.com>
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On Thu, Apr 02, 2015 at 11:42:43AM -0400, Chris Metcalf wrote:
> OK, I will respin v2 of the patch as follows:
> 
> - Provide a watchdog_cpumask as suggested by Don.
> - On a non-NO_HZ_FULL build, it defaults to cpu_possible as normal
> - On a NO_HZ_FULL build, it defaults to the housekeeping cpus

Ah note that NO_HZ_FULL is only the capability. Nohz full is actually
only running if the nohz_full parameter is passed (or NO_HZ_FULL_ALL=y).

And now generalist distros enable NO_HZ_FULL so that anybody can use it.

So better check tick_nohz_full_enabled() instead of the CONFIG.

Thanks.


> - If the mask is modified, we disable and then re-enable the watchdog,
>   so that the watchdog init code can exit() the appropriate threads as
>   they start up
> 
> This should address the various concerns that have been raised.
> 
> -- 
> Chris Metcalf, EZChip Semiconductor
> http://www.ezchip.com
>