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Date: Sun, 13 Feb 2005 17:01:19 -0600
From: Alan Cox <alc@cs.rice.edu>
To: Alan Cox <alc@FreeBSD.org>
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Subject: Re: cvs commit: src/sys/dev/md md.c
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On Sun, Feb 13, 2005 at 09:51:50PM +0000, Alan Cox wrote:
> alc         2005-02-13 21:51:50 UTC
> 
>   FreeBSD src repository
> 
>   Modified files:
>     sys/dev/md           md.c 
>   Log:
>   Request a CPU private mapping from sf_buf_alloc().  If the swap-backed
>   memory disk is larger than the number of available sf_bufs, this improves
>   performance on SMPs by eliminating interprocessor TLB shootdowns.  For
>   example, with 6656 sf_bufs, the default on my test machine, and a 256MB
>   swap-backed memory disk, I see the command
>   "dd if=/dev/md0 of=/dev/null bs=64k" achieve ~489MB/sec with the default,
>   shared mappings, and ~587MB/sec with CPU private mappings.
>   
>   Revision  Changes    Path
>   1.153     +6 -1      src/sys/dev/md/md.c

For completeness, I'll add that with a uniprocessor kernel on the same
machine, this test achieves a bandwidth of ~827MB/sec.

Alan