From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755525Ab2IUN0K (ORCPT ); Fri, 21 Sep 2012 09:26:10 -0400 Received: from casper.infradead.org ([85.118.1.10]:57738 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754707Ab2IUN0I (ORCPT ); Fri, 21 Sep 2012 09:26:08 -0400 Message-ID: <505C6AD4.6030206@kernel.dk> Date: Fri, 21 Sep 2012 15:25:40 +0200 From: Jens Axboe MIME-Version: 1.0 To: Tejun Heo CC: Joseph Glanville , cgroups , Vivek Goyal , linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] block: lift the initial queue bypass mode on blk_register_queue() instead of blk_init_allocated_queue() 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> <20120920210852.GC7264@google.com> In-Reply-To: <20120920210852.GC7264@google.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/20/2012 11:08 PM, Tejun Heo wrote: > 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. Agree, I'll shove them into for-3.7/core -- Jens Axboe