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

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Message-ID: <20061024100032.GA7085@frankl.hpl.hp.com>
Date:	Tue, 24 Oct 2006 03:00:32 -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

Andi,

On Sat, Oct 21, 2006 at 03:22:53PM +0200, Andi Kleen wrote:
> 
> > I finally found the culprit for this. The current code is wrong for the
> > simple reason that the cpu_idle() function is NOT always the lowest level
> > idle loop function. For enter_idle()/__exit_idle() to work correctly they
> > must be placed in the lowest-level idle loop. The cpu_idle() eventually ends
> > up in the idle() function, but this one may have a loop in it! This is the
> > case when idle()=cpu_default_idle() and idle()=poll_idle(), for instance. 
> 
> Ah now I remember - i had actually fixed that (it was the cleanup-idle-loops
> patch) that moved the loops one level up. But then I disabled the patch
> at the request of Andrew because it conflicted with some ACPI idle changes.
> 
> I'll readd it for .20, then things should be ok.
> 

Ok, that's good. In the meantime, I need to produce the i386 equivalent.
Given how poll_idle() works (tight loop), I don't think we can just add
enter_idle()/exit_idle() around the loop, we also need to cover the interrupt
handlers, because that is the only place where we can catch activity considered
useful.

-- 
-Stephane
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