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SubjectRe: [PATCH RESEND 0/1] AHCI: Optimize interrupt processing
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On Wed, 2013-07-17 at 18:19 +0200, Alexander Gordeev wrote:
> 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.

Mmmmmm.

The call to blk_queue_bounce() exists within blk_mq_make_request(), but
AFAICT this should still be getting invoked regardless of if the struct
request is dispatched into blk-mq via the modified blk_execute_rq() ->
blk_execute_rq_nowait() -> blk_mq_insert_request() codepath, or directly
via blk_mq_execute_rq()..

Jens..?

>
> 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.

Most certainly. ;)

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

AFAICT, getting an initial conversion of libata up does not depend upon
this specific issue being addressed first. I could be wrong however..

>
> > 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!
>

Sure. I should have a few extra cycles to hack on this over the
weekend.

Also, thinking about this some more, trying to convert ahci to scsi-mq
first (using QEMU emulation), while keeping a rootfs on PIIX_IDE might
make debugging slightly easier..

--nab



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