From: Wu Fengguang <fengguang.wu@intel.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Jan Kara <jack@suse.cz>, Christoph Hellwig <hch@lst.de>,
Trond Myklebust <Trond.Myklebust@netapp.com>,
Dave Chinner <david@fromorbit.com>, Theodore Ts'o <tytso@mit.edu>,
Chris Mason <chris.mason@oracle.com>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Mel Gorman <mel@csn.ul.ie>, Rik van Riel <riel@redhat.com>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
Greg Thelen <gthelen@google.com>,
Minchan Kim <minchan.kim@gmail.com>,
Vivek Goyal <vgoyal@redhat.com>,
Andrea Righi <arighi@develer.com>,
Balbir Singh <balbir@linux.vnet.ibm.com>,
linux-mm <linux-mm@kvack.org>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 19/27] writeback: dirty throttle bandwidth control
Date: Mon, 7 Mar 2011 13:34:41 -0800 [thread overview]
Message-ID: <20110307213441.GA22237@localhost> (raw)
In-Reply-To: <20110303074951.143474038@intel.com>
On Thu, Mar 03, 2011 at 02:45:24PM +0800, Wu, Fengguang wrote:
> balance_dirty_pages() has been using a very simple and robust threshold
> based throttle scheme. It automatically limits the dirty rate down,
> however in a very bumpy way that constantly block the dirtier tasks for
> hundreds of milliseconds on a local ext4.
To get an idea of what exactly is going on in the current kernel, I
back ported the balance_dirty_pages and global_page_state trace events
to 2.6.38-rc7 and run the same test cases. The resulted graphs are
pretty striking.
In the worst NFS cases, the pause time frequently go up to 20-30 seconds,
and the dirty progress is rather bumpy.
1-dd case
http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/dirty-throttling-v6/vanilla/NFS/nfs-1dd-1M-8p-2945M-20%25-2.6.38-rc7+-2011-03-07-23-14/balance_dirty_pages-pause.png
http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/dirty-throttling-v6/vanilla/NFS/nfs-1dd-1M-8p-2945M-20%25-2.6.38-rc7+-2011-03-07-23-14/global_dirtied_written.png
8-dd case
http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/dirty-throttling-v6/vanilla/NFS/nfs-8dd-1M-8p-2945M-20%25-2.6.38-rc7+-2011-03-07-23-26/balance_dirty_pages-pause.png
http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/dirty-throttling-v6/vanilla/NFS/nfs-8dd-1M-8p-2945M-20%25-2.6.38-rc7+-2011-03-07-23-26/balance_dirty_pages-task-bw.png
The writes to USB key starts with a long 30 seconds pause, followed by
many ~2 seconds long pauses for ext4. XFS is better; btrfs performs the
best, however can still have 7s and 2s long delays.
http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/dirty-throttling-v6/vanilla/1UKEY+1HDD-3G/ext4-1dd-1M-8p-2945M-20%25-2.6.38-rc7+-2011-03-07-23-34/balance_dirty_pages-pause.png
http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/dirty-throttling-v6/vanilla/1UKEY+1HDD-3G/xfs-1dd-1M-8p-2945M-20%25-2.6.38-rc7+-2011-03-07-23-56/balance_dirty_pages-pause.png
http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/dirty-throttling-v6/vanilla/1UKEY+1HDD-3G/btrfs-1dd-1M-8p-2945M-20%25-2.6.38-rc7+-2011-03-08-00-14/balance_dirty_pages-pause.png
For the normal writes to HDD, ext4 has some >300ms pause times in 1-dd
case, >600ms for 2-dd case, and >2s for 8-dd case. The pause time
roughly deteriorates proportionally with the number of concurrent dd tasks.
http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/dirty-throttling-v6/vanilla/4G/ext4-1dd-1M-8p-3911M-20%25-2.6.38-rc7+-2011-03-07-22-15/balance_dirty_pages-pause.png
http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/dirty-throttling-v6/vanilla/4G/ext4-2dd-1M-8p-3911M-20%25-2.6.38-rc7+-2011-03-07-22-22/balance_dirty_pages-pause.png
http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/dirty-throttling-v6/vanilla/4G/ext4-8dd-1M-8p-3911M-20%25-2.6.38-rc7+-2011-03-07-22-30/balance_dirty_pages-pause.png
XFS performs similarly
http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/dirty-throttling-v6/vanilla/4G/xfs-8dd-1M-8p-3911M-20%25-2.6.38-rc7+-2011-03-07-22-08/balance_dirty_pages-pause.png
http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/dirty-throttling-v6/vanilla/4G/xfs-8dd-1M-8p-3911M-20%25-2.6.38-rc7+-2011-03-07-22-08/balance_dirty_pages-task-bw.png
btrfs is better, typically has 1-2s max pause time in 8-dd case
http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/dirty-throttling-v6/vanilla/4G/btrfs-8dd-1M-8p-3911M-20%25-2.6.38-rc7+-2011-03-07-21-48/balance_dirty_pages-pause.png
The long pause times will obviously ruin user experiences. It may also
hurt performance. For example, if the dirtier is a simple "cp" or
"scp", the long pause time will break the readahead pipeline or the
network pipeline, leading to moments of underutilized disk/network
bandwidth.
Comparing to the above graphs, this patchset is able to keep latency
under control (less than the configured 200ms max pause time) in all
known cases, whether it be 1-dd or 1000-dd, on local file systems,
over NFS or on USB key.
8-dd case
http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/dirty-throttling-v6/vanilla/4G/ext4-8dd-1M-8p-3911M-20%25-2.6.38-rc7+-2011-03-07-22-30/balance_dirty_pages-task-bw.png
http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/dirty-throttling-v6/4G/xfs-8dd-1M-8p-3927M-20%25-2.6.38-rc6-dt6+-2011-02-27-23-18/balance_dirty_pages-task-bw.png
128-dd case
http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/dirty-throttling-v6/4G/xfs-128dd-1M-8p-3927M-20%25-2.6.38-rc6-dt6+-2011-02-27-23-25/balance_dirty_pages-pause.png
http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/dirty-throttling-v6/4G/xfs-128dd-1M-8p-3927M-20%25-2.6.38-rc6-dt6+-2011-02-27-23-25/balance_dirty_pages-task-bw.png
1000-dd case
http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/dirty-throttling-v6/10SSD-RAID0-64G/xfs-1000dd-1M-64p-64288M-20%25-2.6.38-rc6-dt6+-2011-02-28-10-40/balance_dirty_pages-pause.png
UKEY
http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/dirty-throttling-v6/1UKEY+1HDD-3G/ext4-1dd-1M-8p-2975M-20%25-2.6.38-rc6-dt6+-2011-02-28-20-21/balance_dirty_pages-pause.png
http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/dirty-throttling-v6/1UKEY+1HDD-3G/xfs-4dd-1M-8p-2945M-20%25-2.6.38-rc5-dt6+-2011-02-22-09-27/balance_dirty_pages-pause.png
NFS
http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/dirty-throttling-v6/NFS/nfs-1dd-1M-8p-2945M-20%25-2.6.38-rc6-dt6+-2011-02-22-21-09/balance_dirty_pages-pause.png
http://www.kernel.org/pub/linux/kernel/people/wfg/writeback/dirty-throttling-v6/NFS/nfs-8dd-1M-8p-2945M-20%25-2.6.38-rc6-dt6+-2011-02-22-21-22/balance_dirty_pages-pause.png
Thanks,
Fengguang
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next prev parent reply other threads:[~2011-03-07 21:36 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-03 6:45 [PATCH 00/27] IO-less dirty throttling v6 Wu Fengguang
2011-03-03 6:45 ` [PATCH 01/27] writeback: add bdi_dirty_limit() kernel-doc Wu Fengguang
2011-03-03 6:45 ` [PATCH 02/27] writeback: avoid duplicate balance_dirty_pages_ratelimited() calls Wu Fengguang
2011-03-03 6:45 ` [PATCH 03/27] writeback: skip balance_dirty_pages() for in-memory fs Wu Fengguang
2011-03-03 6:45 ` [PATCH 04/27] writeback: reduce per-bdi dirty threshold ramp up time Wu Fengguang
2011-03-03 6:45 ` [PATCH 05/27] btrfs: avoid duplicate balance_dirty_pages_ratelimited() calls Wu Fengguang
2011-03-03 6:45 ` [PATCH 06/27] btrfs: lower the dirty balance poll interval Wu Fengguang
2011-03-04 6:22 ` Dave Chinner
2011-03-04 7:57 ` Wu Fengguang
2011-03-03 6:45 ` [PATCH 07/27] btrfs: wait on too many nr_async_bios Wu Fengguang
2011-03-03 6:45 ` [PATCH 08/27] nfs: dirty livelock prevention is now done in VFS Wu Fengguang
2011-03-03 6:45 ` [PATCH 09/27] nfs: writeback pages wait queue Wu Fengguang
2011-03-03 16:07 ` Peter Zijlstra
2011-03-04 1:53 ` Wu Fengguang
2011-03-03 16:08 ` Peter Zijlstra
2011-03-04 2:01 ` Wu Fengguang
2011-03-04 9:10 ` Peter Zijlstra
2011-03-04 9:26 ` Peter Zijlstra
2011-03-04 14:38 ` Wu Fengguang
2011-03-04 14:41 ` Peter Zijlstra
2011-03-03 6:45 ` [PATCH 10/27] nfs: limit the commit size to reduce fluctuations Wu Fengguang
2011-03-03 6:45 ` [PATCH 11/27] nfs: limit the commit range Wu Fengguang
2011-03-03 6:45 ` [PATCH 12/27] nfs: lower writeback threshold proportionally to dirty threshold Wu Fengguang
2011-03-03 6:45 ` [PATCH 13/27] writeback: account per-bdi accumulated written pages Wu Fengguang
2011-03-03 6:45 ` [PATCH 14/27] writeback: account per-bdi accumulated dirtied pages Wu Fengguang
2011-03-03 6:45 ` [PATCH 15/27] writeback: bdi write bandwidth estimation Wu Fengguang
2011-03-03 6:45 ` [PATCH 16/27] writeback: smoothed global/bdi dirty pages Wu Fengguang
2011-03-03 6:45 ` [PATCH 17/27] writeback: smoothed dirty threshold and limit Wu Fengguang
2011-03-03 6:45 ` [PATCH 18/27] writeback: enforce 1/4 gap between the dirty/background thresholds Wu Fengguang
2011-03-03 6:45 ` [PATCH 19/27] writeback: dirty throttle bandwidth control Wu Fengguang
2011-03-07 21:34 ` Wu Fengguang [this message]
2011-03-29 21:08 ` Wu Fengguang
2011-03-03 6:45 ` [PATCH 20/27] writeback: IO-less balance_dirty_pages() Wu Fengguang
2011-03-03 6:45 ` [PATCH 21/27] writeback: show bdi write bandwidth in debugfs Wu Fengguang
2011-03-03 6:45 ` [PATCH 22/27] writeback: trace dirty_throttle_bandwidth Wu Fengguang
2011-03-03 6:45 ` [PATCH 23/27] writeback: trace balance_dirty_pages Wu Fengguang
2011-03-03 6:45 ` [PATCH 24/27] writeback: trace global_dirty_state Wu Fengguang
2011-03-03 6:45 ` [PATCH 25/27] writeback: make nr_to_write a per-file limit Wu Fengguang
2011-03-03 6:45 ` [PATCH 26/27] writeback: scale IO chunk size up to device bandwidth Wu Fengguang
2011-03-03 6:45 ` [PATCH 27/27] writeback: trace writeback_single_inode Wu Fengguang
2011-03-03 20:12 ` [PATCH 00/27] IO-less dirty throttling v6 Vivek Goyal
2011-03-03 20:48 ` Vivek Goyal
2011-03-04 9:06 ` Wu Fengguang
2011-04-04 18:12 ` async write IO controllers Wu Fengguang
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