Re: cfq: depth 4 reached, tagging now on

Lee Revell
2005-02-22T21:10:54Z

On Mon, 2005-02-21 at 09:20 +0100, Jens Axboe wrote:
> 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?)?
>

Yes, this is an all SCSI system using the aic7xxx driver.

> 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.
>

OK. Then the multiple messages were CFQ enabling TCQ for the different
drives.

Lee