From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755487Ab2ITVI7 (ORCPT ); Thu, 20 Sep 2012 17:08:59 -0400 Received: from mail-pb0-f46.google.com ([209.85.160.46]:62956 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752678Ab2ITVI5 (ORCPT ); Thu, 20 Sep 2012 17:08:57 -0400 Date: Thu, 20 Sep 2012 14:08:52 -0700 From: Tejun Heo To: Jens Axboe Cc: Joseph Glanville , cgroups , Vivek Goyal , linux-kernel@vger.kernel.org Subject: [PATCH 1/2] block: lift the initial queue bypass mode on blk_register_queue() instead of blk_init_allocated_queue() Message-ID: <20120920210852.GC7264@google.com> References: <20120919194231.GF31860@redhat.com> <20120920183153.GI28934@google.com> <20120920184219.GH4681@redhat.com> <20120920191716.GI4681@redhat.com> <20120920192038.GJ28934@google.com> <20120920195759.GK4681@redhat.com> <20120920201815.GB7264@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120920201815.GB7264@google.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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: Vivek Goyal Cc: stable@vger.kernel.org --- Jens, while these are fixes, I think it isn't extremely urgent and routing these through 3.7-rc1 should be enough. Thanks. block/blk-core.c | 7 ++----- block/blk-sysfs.c | 6 ++++++ 2 files changed, 8 insertions(+), 5 deletions(-) --- a/block/blk-core.c +++ b/block/blk-core.c @@ -608,8 +608,8 @@ struct request_queue *blk_alloc_queue_no /* * 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); @@ -714,9 +714,6 @@ blk_init_allocated_queue(struct request_ return NULL; blk_queue_congestion_threshold(q); - - /* all done, end the initial bypass */ - blk_queue_bypass_end(q); return q; } EXPORT_SYMBOL(blk_init_allocated_queue); --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -527,6 +527,12 @@ int blk_register_queue(struct gendisk *d 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;