linux-kernel - Re: [QUERY]: Is using CPU hotplug right for isolating CPUs?

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Message-ID: <20140115171704.GB21574@localhost.localdomain>
Date:	Wed, 15 Jan 2014 18:17:06 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Kevin Hilman <khilman@...aro.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Amit Kucheria <amit.kucheria@...aro.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
	Linaro Networking <linaro-networking@...aro.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [QUERY]: Is using CPU hotplug right for isolating CPUs?

On Wed, Jan 15, 2014 at 02:57:36PM +0530, Viresh Kumar wrote:
> Hi Again,
> 
> I am now successful in isolating a CPU completely using CPUsets,
> NO_HZ_FULL and CPU hotplug..
> 
> My setup and requirements for those who weren't following the
> earlier mails:
> 
> For networking machines it is required to run data plane threads on
> some CPUs (i.e. one thread per CPU) and these CPUs shouldn't be
> interrupted by kernel at all.
> 
> Earlier I tried CPUSets with NO_HZ by creating two groups with
> load_balancing disabled between them and manually tried to move
> all tasks out to CPU0 group. But even then there were interruptions
> which were continuously coming on CPU1 (which I am trying to
> isolate). These were some workqueue events, some timers (like
> prandom), timer overflow events (As NO_HZ_FULL pushes hrtimer
> to long ahead in future, 450 seconds, rather than disabling them
> completely, and these hardware timers were overflowing their
> counters after 90 seconds on Samsung Exynos board).

Are you sure about that? NO_HZ_FULL shouldn't touch much hrtimers.
Those are independant from the tick.

Although some of them seem to rely on the softirq, but that seem to
concern the tick hrtimer only.
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