Message-ID: <551D8769.5030100@ezchip.com>
Date: Thu, 2 Apr 2015 14:16:09 -0400
From: Chris Metcalf <cmetcalf@ezchip.com>
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To: Peter Zijlstra <peterz@infradead.org>
CC: Frederic Weisbecker <fweisbec@gmail.com>, 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>,
        Ulrich Obergfell <uobergfe@redhat.com>,
        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>, <linux-kernel@vger.kernel.org>,
        Jonathan Corbet <corbet@lwn.net>, <linux-doc@vger.kernel.org>
Subject: Re: [PATCH v3] watchdog: add watchdog_cpumask sysctl to assist nohz
References: <1427741465-15747-1-git-send-email-cmetcalf@ezchip.com> <20150331072502.GA16754@gmail.com> <551AE7D4.3020608@ezchip.com> <20150402133502.GA175361@redhat.com> <551D48F9.6090101@ezchip.com> <20150402141527.GD175361@redhat.com> <20150402153827.GC10357@lerouge> <551D6373.2030000@ezchip.com> <20150402164845.GD10357@lerouge> <1427996368-2199-1-git-send-email-cmetcalf@ezchip.com> <20150402180626.GG23123@twins.programming.kicks-ass.net>
In-Reply-To: <20150402180626.GG23123@twins.programming.kicks-ass.net>
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On 04/02/2015 02:06 PM, Peter Zijlstra wrote:
> On Thu, Apr 02, 2015 at 01:39:28PM -0400, cmetcalf@ezchip.com wrote:
>> @@ -431,6 +434,10 @@ static void watchdog_enable(unsigned int cpu)
>>   	hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
>>   	hrtimer->function = watchdog_timer_fn;
>>   
>> +	/* Exit if the cpu is not allowed for watchdog. */
>> +	if (!cpumask_test_cpu(cpu, watchdog_mask))
>> +		do_exit(0);
>> +
> Ick, that doesn't look right for smpboot threads.

I didn't see a better way to make this happen without adding
a bunch of infrastructure to the smpboot thread mechanism
to use a cpumask other than for_each_online_cpu().  The exit
seems benign in my testing, but I agree it's not the cleanest
way to express what we're trying to do here.

Perhaps something like an optional cpumask_t pointer in
struct smp_hotplug_thread, which if present specifies the
cpus to run on, and otherwise we stick with cpu_online_mask?

-- 
Chris Metcalf, EZChip Semiconductor
http://www.ezchip.com

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