From: James Bottomley <James.Bottomley@SteelEye.com>
To: Johann Lombardi <johann.lombardi@bull.net>
Cc: linux-scsi@vger.kernel.org
Subject: Re: [RFC] scsi: allow to increase the maximum number of sg entries
Date: Wed, 18 Apr 2007 07:32:03 -0400 [thread overview]
Message-ID: <1176895924.3671.100.camel@mulgrave.il.steeleye.com> (raw)
In-Reply-To: <20070418082114.GE13565@lombardij>
On Wed, 2007-04-18 at 10:21 +0200, Johann Lombardi wrote:
> We have observed noticeable performance improvement by using large single
> command data transfers (up to 4MB) with some storage subsystems such as DDN's.
> The patch below adds a new config option (CONFIG_SCSI_LARGE_SG) which allows to
> increase SCSI_MAX_PHYS_SEGMENTS. When enabled, we should get 4MB transfers even
> if the buffers are completely fragmented in physical memory.
> Thanks in advance for any comments.
I don't think so: simply increasing the phys segments has no effect on a
fully fragmented sg list if the hw segments doesn't go up to match it.
Since changing the hw segments necessitates driver work, I'd really like
to see justification in terms of throughput figures versus transfer size
rather than vague assertions that bigger is better.
James
next prev parent reply other threads:[~2007-04-18 11:32 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-04-18 8:21 [RFC] scsi: allow to increase the maximum number of sg entries Johann Lombardi
2007-04-18 11:32 ` James Bottomley [this message]
2007-04-19 6:30 ` Johann Lombardi
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