From owner-freebsd-hackers  Sat Aug  8 23:50:01 1998
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To: Greg Lehey <grog@lemis.com>
cc: John Baldwin <jobaldwi@vt.edu>, FreeBSD Hackers <hackers@FreeBSD.ORG>
Subject: Re: AMD-specific kernel code (was: How long a wait?) 
In-reply-to: Your message of "Sun, 09 Aug 1998 16:08:29 +0930."
             <19980809160829.A11214@freebie.lemis.com> 
From: David Greenman <dg@root.com>
Reply-To: dg@root.com
Date: Sat, 08 Aug 1998 23:49:51 -0700
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>The effect on CPU performance is also noticable:  here are "make
>world" times:
>
>Without write allocate:
>
>real    106m58.441s
>user    63m0.960s
>sys     20m25.035s
>
>With write allocate:
>
>real    114m16.402s
>user    69m41.733s
>sys     17m54.862s
>
>These were only a rough test (I had other stuff running at the same
>time), but in practice this normally only makes about 1 minute
>difference.  I'd guess that the difference *is* real.  Obviously there
>must be a reason for enabling or disabling this behaviour, and I'd
>guess that write allocation is most effective when one process is
>using much CPU time.  'make world' starts thousands of short-lived
>process, and may thus be the worst-case scenario.  In this connection,
>it's also interesting to note that system time was down and user time
>was up with write allocation.
>
>I have patches available.  Does anybody want to commit them?

   Based on the above performance numbers, I'd say no - they appear to be
a pessimization.

-DG

David Greenman
Co-founder/Principal Architect, The FreeBSD Project

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