From mboxrd@z Thu Jan  1 00:00:00 1970
From: Chris Metcalf <cmetcalf@mellanox.com>
Subject: Re: clocksource_watchdog causing scheduling of timers every second
 (was [v13] support "task_isolation" mode)
Date: Wed, 27 Jul 2016 10:12:02 -0400
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To: Christoph Lameter <cl@linux.com>
Cc: Gilad Ben Yossef <giladb@mellanox.com>, Steven Rostedt <rostedt@goodmis.org>, Ingo Molnar <mingo@kernel.org>, Peter Zijlstra <peterz@infradead.org>, Andrew Morton <akpm@linux-foundation.org>, Rik van Riel <riel@redhat.com>, Tejun Heo <tj@kernel.org>, Frederic Weisbecker <fweisbec@gmail.com>, Thomas Gleixner <tglx@linutronix.de>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, Viresh Kumar <viresh.kumar@linaro.org>, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will.deacon@arm.com>, Andy Lutomirski <luto@amacapital.net>, Daniel Lezcano <daniel.lezcano@linaro.org>, linux-doc@vger.kernel.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org
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On 7/27/2016 9:55 AM, Christoph Lameter wrote:
> The critical piece of code is this:
>
>          /*
>           * Cycle through CPUs to check if the CPUs stay synchronized
>           * to each other.
>           */
>          next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
>          if (next_cpu >= nr_cpu_ids)
>                  next_cpu = cpumask_first(cpu_online_mask);
>          watchdog_timer.expires += WATCHDOG_INTERVAL;
>          add_timer_on(&watchdog_timer, next_cpu);
>
>
> Should we just cycle through the cpus that are not isolated? Otherwise we
> need to have some means to check the clocksources for accuracy remotely
> (probably impossible for TSC etc).

That sounds like the right idea - use the housekeeping cpu mask instead of the
cpu online mask.  Should be a straightforward patch; do you want to do that
and test it in your configuration, and I'll include it in the next spin of the
patch series?

Thanks for your testing!

-- 
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com