linux-kernel - Re: [patch]blk-mq: blk_mq_tag_to

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Message-ID: <20140604145803.GA7826@infradead.org>
Date:	Wed, 4 Jun 2014 07:58:03 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Shaohua Li <shli@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [patch]blk-mq: blk_mq_tag_to_rq should handle flush request

On Wed, Jun 04, 2014 at 08:54:23AM -0600, Jens Axboe wrote:
> >It's not as simple as the added code wants to get a queue from the
> >hwctx, which we can't get at.  I was planning to look into this, but
> >there are various other regressions in the recent block updates that I
> >need to fix before I can even test a tree with this one reverted.
> 
> Which regressions? Performance or crashes?

Both.  I've tracked down the SCSI boot crash and you'll have a patch for
that soon, still working on bisecting the performance crawl, but I'm
getting close.

> >If you can get to sorting this out soon I'd love you to handle it,
> >otherwise I'll look into it as soon as I can.
> 
> Just took a look at it, but I don't see the problematic path. I'm
> looking at wip-9.

scsi_mq_find_tag only gets the scsi host, which may have multiple
queues.  When called from scsi_find_tag we actually have a scsi device,
so that's not an issue, but when called from scsi_host_find_tag the
driver only provides the host.

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