From 749fefe6778e98dfefe3b8bb72a93875196ec554 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Thu, 20 Sep 2012 14:08:52 -0700 Subject: [PATCH] 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 Reported-by: Joseph Glanville Cc: stable@vger.kernel.org Acked-by: Vivek Goyal Signed-off-by: Jens Axboe --- 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 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; -- GitLab