linux-kernel - Re: [.32-rc3] scheduler: iwlagn consistently high in "waiting for CPU"

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Message-ID: <20091008080936.5f3b0e1b@infradead.org>
Date:	Thu, 8 Oct 2009 08:09:36 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Frans Pop <elendil@...net.nl>
Cc:	Mike Galbraith <efault@....de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-wireless@...r.kernel.org
Subject: Re: [.32-rc3] scheduler: iwlagn consistently high in "waiting for
 CPU"

On Thu, 8 Oct 2009 16:55:36 +0200
Frans Pop <elendil@...net.nl> wrote:
> > It turns out that on x86, these two 'opportunistic' timers only
> > get checked when another "real" timer happens.
> > These opportunistic timers have the objective to save power by
> > hitchhiking on other wakeups, as to avoid CPU wakeups by themselves
> > as much as possible.
> 
> This patch makes quite a difference for me. iwlagn and phy0 now 
> consistently show at ~10 ms or lower.\

most excellent

 
> I do still get occasional high latencies, but those are for things
> like "[rpc_wait_bit_killable]" or "Writing a page to disk", where I
> guess you'd expect them. Those high latencies are mostly only listed
> for "Global" and don't translate to individual processes.

and they're very different types of latencies, caused by disk and such.


> The ~10 ms I still get for iwlagn and phy0 (and sometimes higher (~30
> ms) for others like Xorg and artsd) is still "Scheduler: waiting for
> cpu'. If it is actually due to (un)interuptable sleep, isn't that a
> misleading label? I directly associated that with scheduler latency.

it's actually the time between wakeup and running, as measured by
scheduler statistics

-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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