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Date: Mon, 08 Jul 2002 13:30:03 +1000
To: Andrew Morton <akpm@zip.com.au>
From: Lincoln Dale <ltd@cisco.com>
Subject: Re: direct-to-BIO for O_DIRECT
Cc: Benjamin LaHaise <bcrl@redhat.com>, Andrea Arcangeli <andrea@suse.de>,
       "Stephen C. Tweedie" <sct@redhat.com>,
       Linus Torvalds <torvalds@transmeta.com>,
       lkml <linux-kernel@vger.kernel.org>, Steve Lord <lord@sgi.com>
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At 08:19 PM 7/07/2002 -0700, Andrew Morton wrote:
>Here's a patch which converts O_DIRECT to go direct-to-BIO, bypassing
>the kiovec layer.  It's followed by a patch which converts the raw
>driver to use the O_DIRECT engine.
>
>CPU utilisation is about the same as the kiovec-based implementation.
>Read and write bandwidth are the same too, for 128k chunks.   But with
>one megabyte chunks, this implementation is 20% faster at writing.
>
>I assume this is because the kiobuf-based implementation has to stop
>and wait for each 128k chunk, whereas this code streams the entire
>request, regardless of its size.
>
>This is with a single (oldish) scsi disk on aic7xxx.  I'd expect the
>margin to widen on higher-end hardware which likes to have more
>requests in flight.

i'll have a go at benchmark-testing these.

now have even bigger hardware than before: 2 x 2gbit/s FC HBAs in multiple 
dual-processor (Dual P3 Xeon 550MHz 2M L2 cache and Dual P3 Xeon 833MHz 
256K L2 cache) boxen, 8 x 15K RPM FC, 28 x 10K RPM SCSI.


cheers,

lincoln.

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