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SubjectRe: [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@redhat.com


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