[PATCH 030/270] block: lift the initial queue bypass mode on blk_register_queue() instead of blk_init_allocated_queue()
Herton Ronaldo Krzesinski
herton.krzesinski at canonical.com
Mon Nov 26 16:55:20 UTC 2012
3.5.7u1 -stable review patch. If anyone has any objections, please let me know.
From: Tejun Heo <tj at kernel.org>
commit 749fefe6778e98dfefe3b8bb72a93875196ec554 upstream.
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
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
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
Signed-off-by: Tejun Heo <tj at kernel.org>
Reported-by: Joseph Glanville <joseph.glanville at orionvm.com.au>
Acked-by: Vivek Goyal <vgoyal at redhat.com>
Signed-off-by: Jens Axboe <axboe at kernel.dk>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski at canonical.com>
block/blk-core.c | 7 ++-----
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 ad39394..96335a7 100644
@@ -598,8 +598,8 @@ 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;
@@ -702,9 +702,6 @@ blk_init_allocated_queue(struct request_queue *q, request_fn_proc *rfn,
/* init elevator */
if (elevator_init(q, NULL))
- /* all done, end the initial bypass */
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index aa41b47..be7edfc 100644
@@ -523,6 +523,12 @@ int blk_register_queue(struct gendisk *disk)
+ * Initialization must be complete by now. Finish the initial
+ * bypass from queue allocation.
ret = blk_trace_init_sysfs(dev);
More information about the kernel-team