From: Jens Axboe <jaxboe@fusionio.com>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"dpshah@google.com" <dpshah@google.com>
Subject: Re: [RFC PATCH 00/14] blk-throttle: lockless bio processing for no throttle rule group
Date: Thu, 19 May 2011 20:33:10 +0200 [thread overview]
Message-ID: <4DD56266.7090209@fusionio.com> (raw)
In-Reply-To: <1305746006-5837-1-git-send-email-vgoyal@redhat.com>
On 2011-05-18 21:13, Vivek Goyal wrote:
> Hi,
>
> Block throttling code takes request queue lock for every incoming bio
> (blk_throtl_bio()). This is true even if there are no throttle rules in
> the group. This is a common case for root cgroup where distributions
> will have throttling support compiled in but a vast majority of users
> will not be specifying throttling rule.
>
> This patch series tries to make bio processing lockless (no requeust
> queue lock), if there are no rules specified for the group. Once
> a bio is submitted, under rcu_read_lock() we search for the group,
> update the stats and release the rcu lock. request queue lock is taken
> only if there are throttling rules specified in the group.
>
> I have made some of the dispatch stats per cpu so that these can be updated
> without taking request queue lock.
>
> On my system for a simple dd as follows, request queue lock acquisition
> count has gone down by 11% roughly.
>
> dd if=/mnt/zerofile-1G of=/dev/null bs=4K iflag=direct
>
> lockstat output vanilla kernel
> -----------------------------
> class name acquisitions holdtime-total
>
> &(&q->__queue_lock)->rlock: 2360944 1850183.07
>
> lockstat output with patched kernel
> -----------------------------------
> class name acquisitions holdtime-total
> &(&q->__queue_lock)->rlock: 2098599 1430478.79
>
>
> I did test on a 4 cpu system doing IO to one SSD. I did not see any
> significant improvement in throughput. I suspect that I never saturated
> the cpus hence I don't see the improvement in throughput. I will see
> if I can get more testing done on this and see if I notice IO throughput
> improvement.
>
> Jens, first patch of the series is already in your for-linus branch. I
> was waiting for it to be pushed to Linus and then I can drop that first
> patch.
Vivek, I get weird things in these patches. In fact I always get on your
patches. = are =3D, =20 some places, and line breaks. Can I ask you to
try and resend it to axboe@kernel.dk just to see if it's the company MTA
screwing things up, or if it's something at your end?
--
Jens Axboe
next prev parent reply other threads:[~2011-05-19 18:33 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-18 19:13 [RFC PATCH 00/14] blk-throttle: lockless bio processing for no throttle rule group Vivek Goyal
2011-05-18 19:13 ` [PATCH 01/14] blk-throttle: Use task_subsys_state() to determine a task's blkio_cgroup Vivek Goyal
2011-05-18 19:13 ` [PATCH 02/14] blk-throttle: Do the new group initialization with the help of a function Vivek Goyal
2011-05-18 19:13 ` [PATCH 03/14] blk-cgroup: move some fields of unaccounted_time file under right config option Vivek Goyal
2011-05-18 19:13 ` [PATCH 04/14] cfq-iosched: Get rid of redundant function parameter "create" Vivek Goyal
2011-05-18 19:13 ` [PATCH 05/14] cfq-iosched: Fix a possible race with cfq cgroup removal code Vivek Goyal
2011-05-18 19:13 ` [PATCH 06/14] blk-cgroup: Allow sleeping while dynamically allocating a group Vivek Goyal
2011-05-18 19:13 ` [PATCH 07/14] blk-throttle: Dynamically allocate root group Vivek Goyal
2011-05-18 19:13 ` [PATCH 08/14] blk-throttle: Introduce a helper function to fill in device details Vivek Goyal
2011-05-18 19:13 ` [PATCH 09/14] blk-throttle: Use helper function to add root throtl group to lists Vivek Goyal
2011-05-18 19:13 ` [PATCH 10/14] blk-throttle: Free up a group only after one rcu grace period Vivek Goyal
2011-05-18 19:13 ` [PATCH 11/14] blk-throttle: Make dispatch stats per cpu Vivek Goyal
2011-05-18 19:13 ` [PATCH 12/14] blk-cgroup: Make 64bit per cpu stats safe on 32bit arch Vivek Goyal
2011-05-18 19:13 ` [PATCH 13/14] blk-cgroup: Make cgroup stat reset path blkg->lock free for dispatch stats Vivek Goyal
2011-05-18 19:13 ` [PATCH 14/14] blk-throttle: Make no throttling rule group processing lockless Vivek Goyal
2011-05-19 18:33 ` Jens Axboe [this message]
2011-05-19 18:44 ` [RFC PATCH 00/14] blk-throttle: lockless bio processing for no throttle rule group Vivek Goyal
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