linux-kernel - Re: [PATCH] x86_64 add missing enter

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Message-ID: <20061016144417.GG15540@frankl.hpl.hp.com>
Date:	Mon, 16 Oct 2006 07:44:17 -0700
From:	Stephane Eranian <eranian@....hp.com>
To:	Andi Kleen <ak@...e.de>
Cc:	linux-kernel@...r.kernel.org, akpm@...l.org
Subject: Re: [PATCH] x86_64 add missing enter_idle() calls

On Mon, Oct 16, 2006 at 04:36:52PM +0200, Andi Kleen wrote:
> 
> > With the original code, the number of callbacks you see for IDLE_START and
> > IDLE_STOP is not too obvious.
> > 
> > On an idle system Opteron 250 with HZ=250, one would expect to see for a 10s duration:
> > 	- for CPU0      : IDLE_START = IDLE_STOP = about 5000 calls
> > 	- for other CPUs: IDLE_START = IDLE_STOP = about 2500  calls
> 
> Yes.
> 
> > With the original code, you get the following number of calls:
> > 
> > CPU0.IDLE_START = 44 (enter_idle)
> > CPU0.IDLE_STOP  = 5206 (exit_idle)
> > 
> > CPU1.IDLE_START = 27 (enter_idle)
> > CPU1.IDLE_STOP  = 2528 (exit_idle)
> > 
> > Now, of course, you may get "batched" interrupts where you do not return to idle
> > before you process the next interrupt. But the difference seems quite high here.
> 
> Shouldn't happen for timer interrupts.
> > 
> > Do you have an explanation for this?
> 
> Hmm, the last time I fixed this when you complained (post .18) i added a counter for 
> entry/exit and verified that it was balanced. I haven't rechecked since then.
> I don't know why your numbers are off. You're using the latest git tree, right?
>  
No, I am still using 2.6.18. I saw your change in git (thanks for that). I need to try
with this tree and see what happens.

Thanks.

-- 
-Stephane
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