linux-kernel - Re: [PATCH 14/18] 2.6.17.9 perfmon2 patch for review: new i386 files

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Message-Id: <200608251718.47698.ak@suse.de>
Date:	Fri, 25 Aug 2006 17:18:47 +0200
From:	Andi Kleen <ak@...e.de>
To:	eranian@....hp.com
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 14/18] 2.6.17.9 perfmon2 patch for review: new i386 files

On Friday 25 August 2006 17:00, Stephane Eranian wrote:

> > > > BTW you might be able to simplify some of your code by exploiting
> > > > those. i386 currently doesn't have them, but i wouldn't see a problem
> > > > with adding them there too.
> > > >  
> > > I think I will drop the EXCL_IDLE feature given that most PMU stop
> > > counting when you go low-power. The feature does not quite do what
> > > we want because it totally exclude the idle from monitoring, yet
> > > the idle may be doing useful kernel work, such as fielding interrupts.
> > 
> > Ok fine. Anything that makes the code less complex is good.
> > Currently it is very big and hard to understand.
> > 
> > (actually at least one newer Intel system I saw seemed to continue counting
> > in idle, but that might have been a specific quirk)
> > 
> 
> Yes, that's my fear, we may get inconsistent behaviors across architectures.

It's already the case with idle=poll vs not.

> I think the only way to ensure some consistency would be to use the
> enter/exit_idle callbacks you mentioned assuming those would be available for
> all architectures.  With this, we could guarantee that we are not monitoring
> usless execution (including low-power mode) simply because we would explicitely
> stop monitoring on enter_idle() and restart monitoring on exit_idle().

Or better account for it using RDTSC because often people want their numbers to add up to 100%
when doing global accounting.  For other events than cycles=time it is not needed
because they don't happen by definition in idle.

This was one reason I added the hooks because it was a FAQ on oprofile

If you want them for i386 just send a patch to port them.
 
-andi
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