diff options
authorTejun Heo <tj@kernel.org>2012-09-20 14:08:52 -0700
committerJens Axboe <axboe@kernel.dk>2012-09-21 15:32:57 +0200
commit749fefe6778e98dfefe3b8bb72a93875196ec554 (patch)
parent66ba32dc167202c3cf8c86806581a9393ec7f488 (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>
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;
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;

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