diff options
| author | Tejun Heo <tj@kernel.org> | 2012-09-20 14:08:52 -0700 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2012-09-21 15:32:57 +0200 |
| commit | 749fefe6778e98dfefe3b8bb72a93875196ec554 (patch) | |
| tree | 7e3b2f2fb6e7bec5579a58e9f0c33fb614e69d80 /block | |
| parent | 66ba32dc167202c3cf8c86806581a9393ec7f488 (diff) | |
block: lift the initial queue bypass mode on blk_register_queue() instead of blk_init_allocated_queue()
b82d4b197c ("blkcg: make request_queue bypassing on allocation") made
request_queues bypassed on allocation to avoid switching on and off
bypass mode on a queue being initialized. Some drivers allocate and
then destroy a lot of queues without fully initializing them and
incurring bypass latency overhead on each of them could add upto
significant overhead.
Unfortunately, blk_init_allocated_queue() is never used by queues of
bio-based drivers, which means that all bio-based driver queues are in
bypass mode even after initialization and registration complete
successfully.
Due to the limited way request_queues are used by bio drivers, this
problem is hidden pretty well but it shows up when blk-throttle is
used in combination with a bio-based driver. Trying to configure
(echoing to cgroupfs file) blk-throttle for a bio-based driver hangs
indefinitely in blkg_conf_prep() waiting for bypass mode to end.
This patch moves the initial blk_queue_bypass_end() call from
blk_init_allocated_queue() to blk_register_queue() which is called for
any userland-visible queues regardless of its type.
I believe this is correct because I don't think there is any block
driver which needs or wants working elevator and blk-cgroup on a queue
which isn't visible to userland. If there are such users, we need a
different solution.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Joseph Glanville <joseph.glanville@orionvm.com.au>
Cc: stable@vger.kernel.org
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block')
| -rw-r--r-- | block/blk-core.c | 7 | ||||
| -rw-r--r-- | block/blk-sysfs.c | 6 |
2 files changed, 8 insertions, 5 deletions
diff --git a/block/blk-core.c b/block/blk-core.c index 3b080541098e..80e29c90723c 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -608,8 +608,8 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id) /* * A queue starts its life with bypass turned on to avoid * unnecessary bypass on/off overhead and nasty surprises during - * init. The initial bypass will be finished at the end of - * blk_init_allocated_queue(). + * init. The initial bypass will be finished when the queue is + * registered by blk_register_queue(). */ q->bypass_depth = 1; __set_bit(QUEUE_FLAG_BYPASS, &q->queue_flags); @@ -712,9 +712,6 @@ blk_init_allocated_queue(struct request_queue *q, request_fn_proc *rfn, /* init elevator */ if (elevator_init(q, NULL)) return NULL; - - /* all done, end the initial bypass */ - blk_queue_bypass_end(q); return q; } EXPORT_SYMBOL(blk_init_allocated_queue); diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index 247dbfd42621..ce6204608822 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -561,6 +561,12 @@ int blk_register_queue(struct gendisk *disk) if (WARN_ON(!q)) return -ENXIO; + /* + * Initialization must be complete by now. Finish the initial + * bypass from queue allocation. + */ + blk_queue_bypass_end(q); + ret = blk_trace_init_sysfs(dev); if (ret) return ret; |