Date: Mon, 21 Feb 2005 09:20:44 +0100
From: Jens Axboe <axboe@suse.de>
To: Lee Revell <rlrevell@joe-job.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: cfq: depth 4 reached, tagging now on
Message-ID: <20050221082044.GW4056@suse.de>
References: <1108846748.10705.31.camel@krustophenia.net>
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On Sat, Feb 19 2005, Lee Revell wrote:
> Starting around 2.6.11-rc4 I get this printk during the boot process
> after kjournald starts, and again if I stress the filesystem.
> 
> cfq: depth 4 reached, tagging now on
> 
> Is this printk intentional?  I am sure users will wonder about it,
> especially because (presumably) cfq turns tagging off at some point in
> between, and doesn't say anything about it.

It is intentional, but could be supressed. But I'm wondering if the
accounting change introduced a bug - what hardware are you using cfq on
(ie does it actually do tagged command queueing, is it SCSI?)?

It's a one-time message. CFQ starts out assuming the drive doesn't do
TCQ, if the driver depth goes beyond a defined limit (4), it will assume
that the hardware can do tagged queueing and change its internal
accounting accordingly. The setting stays that way, it's not a
transitional state.

-- 
Jens Axboe

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