linux-kernel - Re: Too many timer interrupts in NO

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Message-ID: <20080302115709.30403490@laptopd505.fenrus.org>
Date:	Sun, 2 Mar 2008 11:57:09 -0800
From:	Arjan van de Ven <arjan@...radead.org>
To:	svaidy@...ux.vnet.ibm.com
Cc:	discuss@...sWatts.org,
	Linux-pm mailing list <linux-pm@...ts.linux-foundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>, venkatesh.pallipadi@...el.com,
	tglx@...utronix.de, suresh.b.siddha@...el.com,
	Gautham R Shenoy <ego@...ibm.com>,
	Chanda Sethia <chanda.sethia@...ibm.com>
Subject: Re: Too many timer interrupts in NO_HZ

On Mon, 3 Mar 2008 01:18:13 +0530
Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com> wrote:

> Hi,
> 
> I am trying to play around with the tickless kernel and
> sched_mc_power_savings tunables to increase the idle duration of the
> CPU in an SMP server.  sched_mc_power_savings provides good
> consolidation of long running jobs when the system is lightly loaded.
> However I am interested to see CPU idle times for couple minutes on
> atleast few CPUs in an completely idle SMP system.
> 
> I have posted related instrumentation results at
> http://lkml.org/lkml/2008/1/8/243
> 
> The experimental setup is identical.  Just that I have tried to
> collect more data and also bias the wakeup logic.
> 
> The kernel is 2.6.25-rc3 with NO_HZ, SCHED_MC, HIGH_RES_TIMERS, and
> HPET turned on.
> 
> I have tried to collect interesting data from tick-sched.c, sched.c
> and softirq.c.
> 
> As suggested by Ingo in the previous thread, I have hacked the sched.c
> try_to_wake_up logic so that I can force all wake-ups to happen on
> CPU0.  This is just and experiment, in reality we will have to
> carefully choose a domain and CPU to bias all wakeups on an idle
> system.


please show us powertop -d output; that way we can at least see sort of what
is going on...
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