linux-kernel - Re: [PATCH] watchdog: nohz: don't run watchdog on nohz

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Date:	Tue, 31 Mar 2015 08:34:17 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Don Zickus <dzickus@...hat.com>
Cc:	cmetcalf@...hip.com, Andrew Morton <akpm@...ux-foundation.org>,
	Andrew Jones <drjones@...hat.com>,
	chai wen <chaiw.fnst@...fujitsu.com>,
	Ingo Molnar <mingo@...nel.org>,
	Ulrich Obergfell <uobergfe@...hat.com>,
	Fabian Frederick <fabf@...net.be>,
	Aaron Tomlin <atomlin@...hat.com>,
	Ben Zhang <benzh@...omium.org>,
	Christoph Lameter <cl@...ux.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Gilad Ben-Yossef <gilad@...yossef.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] watchdog: nohz: don't run watchdog on nohz_full cores

On Tue, 2015-03-31 at 04:04 +0200, Mike Galbraith wrote:

> A bigger deal is the clocksource watchdog methinks.  Measurement
> inspired me to make it dead yesterday.

This is why btw.  Note the alternating sum/s for 1 second samples..
shooting the watchdog makes that a steady 5us.

homer:~ # cgexec -g cpuset:rtcpus taskset -c 3 pert 1
3591.70 MHZ CPU
perturbation threshold 0.013 usecs.
pert/s:        4 >5.61us:        2 min:  0.04 max:  6.89 avg:  3.68 sum/s:    15us overhead: 0.00%
pert/s:        3 >5.34us:        0 min:  0.04 max:  4.01 avg:  1.79 sum/s:     5us overhead: 0.00%
pert/s:        5 >5.33us:        2 min:  0.04 max:  7.34 avg:  3.11 sum/s:    16us overhead: 0.00%
pert/s:        3 >5.08us:        0 min:  0.04 max:  3.87 avg:  1.75 sum/s:     5us overhead: 0.00%
pert/s:        3 >5.18us:        2 min:  1.04 max:  7.16 avg:  5.10 sum/s:    15us overhead: 0.00%                                                                                                             
pert/s:        4 >4.93us:        0 min:  0.04 max:  3.93 avg:  1.33 sum/s:     5us overhead: 0.00%                                                                                                             
pert/s:        6 >4.91us:        2 min:  0.04 max:  7.05 avg:  2.55 sum/s:    15us overhead: 0.00%                                                                                                             
pert/s:        3 >4.70us:        0 min:  0.04 max:  3.73 avg:  1.78 sum/s:     5us overhead: 0.00%

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