Date: Fri, 1 Apr 2005 20:11:05 -0800
From: Paul Jackson <pj@engr.sgi.com>
To: Robert Hancock <hancockr@shaw.ca>
Cc: linux-kernel@vger.kernel.org
Subject: Re: AMD64 Machine hardlocks when using memset
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Robert wrote:
> It does run visibly slower

The x86_64 memset(), both in user space and the kernel, for whatever gcc
I have, and for a current kernel, uses the "repz stos" or "rep stosq"
prefixed instruction for the bulk of the copy.  This combination is a
long running, interruptible Intel string instruction that loops on
itself until the CX register decrements to zero.

Was your windows app using "stos"?

I'll wager a nickel that the actual crash you see comes when the
processor has to handle an interrupt while in the middle of this
instruction.

I'll wager a dime it's hardware, though interrupt activity may be
required to provoke it.

-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@engr.sgi.com> 1.650.933.1373, 1.925.600.0401
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