linux-kernel - Re: [PATCH RESEND 0/1] AHCI: Optimize interrupt processing

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Message-ID: <20130716183207.GA6402@dhcp-26-207.brq.redhat.com>
Date:	Tue, 16 Jul 2013 20:32:08 +0200
From:	Alexander Gordeev <agordeev@...hat.com>
To:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
Cc:	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org,
	linux-ide@...r.kernel.org, Jeff Garzik <jgarzik@...ox.com>,
	Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH RESEND 0/1] AHCI: Optimize interrupt processing

On Fri, Jul 12, 2013 at 10:20:12PM -0700, Nicholas A. Bellinger wrote:
> On Fri, 2013-07-12 at 09:46 +0200, Alexander Gordeev wrote:
> > > > diff --git a/drivers/scsi/scsi-mq.c b/drivers/scsi/scsi-mq.c
> > > > index ca6ff67..d8cc7a4 100644
> > > > --- a/drivers/scsi/scsi-mq.c
> > > > +++ b/drivers/scsi/scsi-mq.c
> > > > @@ -155,6 +155,7 @@ void scsi_mq_done(struct scsi_cmnd *sc)
> > > >  static struct blk_mq_ops scsi_mq_ops = {
> > > >  	.queue_rq	= scsi_mq_queue_rq,
> > > >  	.map_queue	= blk_mq_map_queue,
> > > > +	.timeout	= scsi_times_out,
> > > >  	.alloc_hctx	= blk_mq_alloc_single_hw_queue,
> > > >  	.free_hctx	= blk_mq_free_single_hw_queue,
> > > >  };
> 
> So your actually triggering a blk-mq timeout with ata_piix..?

No.
That is to avoid a NULL-pointer assignment from ->timeout elsewhere.
In fact I return -ENODEV for sr_probe() to not hit it.

> That is why scsi-mq still uses blk_execute_rq() for this reason, and
> this will need be addressed in order to safely use blk_mq_execute_rq()
> in the above context.

Got it.

> Do you have an OOPs backtrace handy to post w/o the last two changes in
> place..?

Attaching the output. No oops actually (due to aforementioned .timeout).

> I *very* much recommend doing the same if at all possible for ata_piix
> scsi-mq development + testing, as you'll want to be very careful when
> using a real file-system on top of this early alpha code.

Thank you for the warning.
Getting to writing CDBs would be of success :)

> --nab
> 

-- 
Regards,
Alexander Gordeev
agordeev@...hat.com

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