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

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Date:	Wed, 17 Jul 2013 18:19:10 +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>,
	linux-scsi <linux-scsi@...r.kernel.org>
Subject: Re: [PATCH RESEND 0/1] AHCI: Optimize interrupt processing

On Tue, Jul 16, 2013 at 02:38:03PM -0700, Nicholas A. Bellinger wrote:
> [    7.927818] scsi_execute(): Calling blk_mq_free_request >>>
> [    7.927826] scsi 0:0:0:0: Direct-Access     ATA      ST9500530NS      CC03 PQ: 0 ANSI: 5
> 
> OK, so INQUIRY response payload is looking as expected here.

Yep. It is not on the top of my head, but I remember something like INQUIRYs
are emulated and thus do not have payload.

> [    7.927960] sd 0:0:0:0: [sda] Sector size 0 reported, assuming 512.
> [    7.927964] sd 0:0:0:0: [sda] 1 512-byte logical blocks: (512 B/512 B)
> [    7.927965] sd 0:0:0:0: [sda] 0-byte physical blocks
> 
> Strange..  READ_CAPACITY appears to be returning a payload as zeros..?

Yep. Because blk_execute_rq() does not put the proper callback and data do
not get copied from sg's to bounce buffer. That is why I tried to use
blk_mq_execute_rq() instead. Once I do that, data start getting read and
booting stops elsewhere.

Of course, I was suspecting that change alone is not valid and wondered
about the status of scsi-mq in the first place, and if more changes are
coming.

So I it turns out "req->errors + req->resid_len" issue (you described
earlier) needs to be addressed before going forward with libata (only?).

> Not sure why yet some control CDBs are getting back the expected
> payload, while others are returning zeros..

Bio buffers do not get updated from callback.

> Also, looking at the included stack back-trace:

[...]

Thanks a lot for these and other your comments, Nicholas!

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