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Date: Fri, 27 Oct 2000 12:25:49 +0200
From: Andi Kleen <ak@suse.de>
To: Andrew Morton <andrewm@uow.edu.au>
Cc: Andi Kleen <ak@suse.de>, Alexander Viro <viro@math.psu.edu>,
        "Jeff V. Merkey" <jmerkey@timpanogas.org>, kumon@flab.fujitsu.co.jp,
        Rik van Riel <riel@conectiva.com.br>, linux-kernel@vger.kernel.org
Subject: Re: Negative scalability by removal of lock_kernel()?(Was: Strange performance behavior of 2.4.0-test9)
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In-Reply-To: <39F957BC.4289FF10@uow.edu.au>; from andrewm@uow.edu.au on Fri, Oct 27, 2000 at 09:23:56PM +1100
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On Fri, Oct 27, 2000 at 09:23:56PM +1100, Andrew Morton wrote:
> Andi Kleen wrote:
> > 
> > When you have two CPUs contending on common paths it is better to do:
> > [ spinlock stuff ]
> 
> Andi, if the lock_kernel() is removed then the first time the CPUs will butt heads is on a semaphore.  This is much more expensive.
> 
> I bet if acquire_fl_sem() and release_fl_sem() are turned into lock_kernel()/unlock_kernel() then the scalability will come back.

To test your theory it would be enough to watch context switch rates in top



-Andi
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