Date: Mon, 16 Jun 2008 08:30:03 -0400
From: Mathieu Desnoyers <compudj@krystal.dyndns.org>
To: Eduard - Gabriel Munteanu <eduard.munteanu@linux360.ro>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>, tzanussi@gmail.com,
       akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
       righi.andrea@gmail.com
Subject: Re: [PATCH 3/3] relay: Add buffer-only channels; useful for early
	logging.
Message-ID: <20080616123003.GC18561@Krystal>
References: <20080613041013.274ccb28@linux360.ro> <48521C19.6070001@cs.helsinki.fi> <20080613185414.306b4baa@linux360.ro>
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* Eduard - Gabriel Munteanu (eduard.munteanu@linux360.ro) wrote:
> On Fri, 13 Jun 2008 10:04:57 +0300
> Pekka Enberg <penberg@cs.helsinki.fi> wrote:
> 
> > Why do we need to change for_each_online_cpu to for_each_present_cpu?
> > I guess it's because we don't have all the CPUs online at early
> > boot?
> 
> Yes, that's true. Only one CPU is online at that early point.
> 
> > Wouldn't it then be better to implement CPU hotplug support
> > instead?
> 
> It's difficult for me to write such code, as I'm unable to test CPU
> hotplug; my machines are a Turion X2 laptop and a Athlon Barton desktop
> computer. So I can't turn off, or unplug in a software sense, one CPU core.
> Correct me if I'm wrong, but I don't see any way to do that in /sys/devices/system/cpu/
> 

See Documentation/cpu-hotplug.txt

If you need to "emulate" having many CPUs, Xen is always an option.

> But I suppose I could write a patch very carefully, and then submit to
> someone that can test this. Anyway, I'll look into this and try to
> understand the code without being able to test.
> 

Hrm, sounds like a bad idea... please try getting a test setup working,
it will save you a gazillion iterations and let you stress-test your
code.

Mathieu

> 
> 	Eduard
> 

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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