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From: James Bottomley <James.Bottomley@SteelEye.com>
To: Hannes Reinecke <hare@suse.de>
Cc: SCSI Mailing List <linux-scsi@vger.kernel.org>
Subject: Re: Overlapped command error handling
Date: Fri, 03 Feb 2006 09:31:25 -0600	[thread overview]
Message-ID: <1138980685.2830.7.camel@localhost.localdomain> (raw)
In-Reply-To: <43E323BA.8010604@suse.de>

On Fri, 2006-02-03 at 10:34 +0100, Hannes Reinecke wrote:

> Can someone explain to my how having a queue depth of '2' in the non-TCQ
> case can be correct?
> If not, please apply the following patch. Oh, and aic7xxx suffers from
> the same problem, naturally.

Yes, the driver is supposed to be counting both the tagged and untagged
commands outstanding and return SCSI_MLQUEUE_DEVICE_BUSY if the
mid-layer tries to queue over that.

The premise of setting this to 2 is that we always have one command in
progress and one completely prepared ready to fire as soon as the
in-progress one returns.  Jens has postulated that this is no-longer
necessary; we could simply reduce the queue depth to 1 for the non-TCQ
case.  What this would do is transfer the setup work from the sending
process to the block softirq, so it might increase latency in the
non-TCQ case ... but no-one knows for sure.

James



  reply	other threads:[~2006-02-03 15:31 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2006-02-02 13:00 Overlapped command error handling Hannes Reinecke
2006-02-02 15:12 ` James Bottomley
2006-02-03  9:34   ` Hannes Reinecke
2006-02-03 15:31     ` James Bottomley [this message]
  -- strict thread matches above, loose matches on Subject: below --
2006-02-03 11:00 Emmanuel Fusté
2006-02-03 11:13 Emmanuel Fusté
2006-02-04 17:01 Emmanuel Fusté

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