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From: Bernard Blackham <bernard@blackham.com.au>
To: Jeff Garzik <jgarzik@pobox.com>
Cc: Matt <matt@signalz.com>, linux-kernel@vger.kernel.org
Subject: Promise SX8 performance issues and CARM_MAX_Q
Date: Thu, 24 Mar 2005 01:57:07 +0800	[thread overview]
Message-ID: <20050323175707.GA10481@blackham.com.au> (raw)
In-Reply-To: <1101757822.4309.37.camel@schroder.signalz.com>

Hi,

Playing with a recently acquired Promise SX8 card, we've found
similar performance results to Matt's post to lkml a few months back
at http://marc.theaimsgroup.com/?l=linux-kernel&m=110175890323356&w=2

It appears that the driver is only submitting one command at a time
per port, which is at least one cause of the slowdowns. By raising
CARM_MAX_Q from 1 to 3 in drivers/block/sx8.c (it was 3 in an
earlier pre-merge incarnation of carmel.c), we're getting very
notable speed improvements, with no side effects just yet.

Knowing very little about what this change has actually done, I've a
few questions: 

 - Should this be considered dangerous?
 - Why was it taken from 3 to 1?
 - Is CARM_MAX_Q a number defined (or limited) by the hardware?

Thanks in advance,

Bernard.

-- 
 Bernard Blackham <bernard at blackham dot com dot au>

  reply	other threads:[~2005-03-23 17:57 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2004-11-29 19:50 Promise SX8 driver performance Matt
2005-03-23 17:57 ` Bernard Blackham [this message]
2005-03-23 23:16   ` Promise SX8 performance issues and CARM_MAX_Q Jeff Garzik
2005-03-23 23:25     ` Matthew Collins
2005-03-25  4:09       ` Jeff Garzik
2005-03-25  4:47         ` Bernard Blackham
2005-03-26 14:12         ` Bernard Blackham

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