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Subject: Re: smp overhead, and rwlocks considered harmful
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Michael Vergoz <mvergoz@sysdoor.com>
Cc: Andrew Morton <akpm@digeo.com>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Sun, 2003-03-23 at 12:33, Michael Vergoz wrote:
> Hi Andrew,
> 
> I would like to noticed to you that the SMP capacity can't be used on one process under Linux.
> 
> when you run 'time dd if=/dev/zero of=foo bs=1 count=1M', the capacity of 1 processor will
> use since your command sets is executed in ONE process.

Your dd is benchmarking the lock operations in the C library I suspect.
The kernel will happily use both processors and a given syscall can
evne start on one cpu and complete on another, or have the IRQ tasks
executed on its behalf on another CPU.

There are *good* reasons btw for avoiding splitting stuff too far, the
cost of copying data between processor caches is very high.

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