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

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Message-ID: <20130920151915.GC10507@dhcp-26-207.brq.redhat.com>
Date:	Fri, 20 Sep 2013 17:19:16 +0200
From:	Alexander Gordeev <agordeev@...hat.com>
To:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>,
	Jens Axboe <axboe@...nel.dk>
Cc:	Mike Christie <mchristie@...ionio.com>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Jens Axboe <axboe@...nel.dk>, Tejun Heo <tj@...nel.org>,
	linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org,
	Jeff Garzik <jgarzik@...ox.com>,
	linux-scsi <linux-scsi@...r.kernel.org>
Subject: Re: [PATCH RESEND 0/1] AHCI: Optimize interrupt processing

On Thu, Aug 15, 2013 at 07:19:29PM -0700, Nicholas A. Bellinger wrote:
> Ok, here's a bit better idea of what is going on now..
> 
> The problem is that blkdev_issue_flush() -> blk_mq_make_request() ->
> __blk_mq_alloc_request() allocates the first tag, which calls
> blk_insert_flush() -> blk_flush_complete_seq() -> blk_flush_kick() ->
> mq_flush_work() -> blk_mq_alloc_request() to allocate a second tag for
> the struct request that actually gets dispatched into scsi-mq as a
> SYCHRONIZE_CACHE command..
> 
> I'm not exactly sure why this double tag usage of struct request is
> occurring, but AFAICT it does happen for every flush, and is not
> specific to the blkdev_issue_flush() codepath..  I'm sure that Jens can
> fill us in on that bit.  ;)

I also played with the double tag using a reserved tag (below).

While it fixes 'fdisk /dev/sda' issue when trying to 'mount /dev/sda1 /mnt'
what appears to be a call to bio->bi_end_io() from the free'd bio hits in.

Not sure if I should pursue the root cause until the whole double-tag
thingy is confirmed.

Jens?


diff --git a/block/blk-mq.c b/block/blk-mq.c
index 6fc1df3..81794dc 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -874,14 +874,14 @@ static void blk_mq_make_request(struct request_queue *q, struct bio *bio)
 	hctx = q->mq_ops->map_queue(q, ctx->cpu);
 
 	trace_block_getrq(q, bio, rw);
-	rq = __blk_mq_alloc_request(hctx, GFP_ATOMIC, false);
+	rq = __blk_mq_alloc_request(hctx, GFP_ATOMIC, is_flush_fua);
 	if (likely(rq))
 		blk_mq_rq_ctx_init(ctx, rq, rw);
 	else {
 		blk_mq_put_ctx(ctx);
 		trace_block_sleeprq(q, bio, rw);
 		rq = blk_mq_alloc_request_pinned(q, rw, __GFP_WAIT|GFP_ATOMIC,
-							false);
+							is_flush_fua);
 		ctx = rq->mq_ctx;
 		hctx = q->mq_ops->map_queue(q, ctx->cpu);
 	}
@@ -1317,6 +1317,9 @@ struct request_queue *blk_mq_init_queue(struct blk_mq_reg *reg,
 		reg->queue_depth = BLK_MQ_MAX_DEPTH;
 	}
 
+	reg->queue_depth++;
+	reg->reserved_tags++;
+
 	ctx = alloc_percpu(struct blk_mq_ctx);
 	if (!ctx)
 		return ERR_PTR(-ENOMEM);

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