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

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Message-Id: <200610161636.52721.ak@suse.de>
Date:	Mon, 16 Oct 2006 16:36:52 +0200
From:	Andi Kleen <ak@...e.de>
To:	eranian@....hp.com
Cc:	linux-kernel@...r.kernel.org, akpm@...l.org
Subject: Re: [PATCH] x86_64 add missing enter_idle() calls


> 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?
 
-Andi

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