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Date: Fri, 27 Oct 2000 21:23:56 +1100
From: Andrew Morton <andrewm@uow.edu.au>
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To: Andi Kleen <ak@suse.de>
CC: 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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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.
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