linux-kernel - Re: [RFC PATCH] Block device bio throttling support [V3]

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Date:	Thu, 16 Sep 2010 00:10:53 -0700
From:	Divyesh Shah <dpshah@...gle.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	linux-kernel@...r.kernel.org, axboe@...nel.dk, nauman@...gle.com,
	guijianfeng@...fujitsu.com
Subject: Re: [RFC PATCH] Block device bio throttling support [V3]

Hi Vivek,
    I took a look at the patches and overall they look good to me.
I'll need to take a closer look at the main throttling patch and the
put on a queue when throttled behavior. Will post comments if any in a
day or so.

-Divyesh

On Wed, Sep 15, 2010 at 2:06 PM, Vivek Goyal <vgoyal@...hat.com> wrote:
>
> Hi,
>
> This is V3 of the bio throttling patches. Following are changes since V2.
>
> - Added the support for throttling in terms of IOPS (READ/WRITE). If one
>  specifies both bandwidth as well as IOPS rules on a device then IO is
>  subjected to both the rules.
>
> - Did few bug fixes.
>
> - Did some cleanups in blk-cgroup code.
>
> Previous version of patches are available here.
>
> [V2] http://lkml.org/lkml/2010/9/7/386
> [V1] http://lkml.org/lkml/2010/9/1/251
>
> Overview
> ========
> Currently CFQ provides the weight based proportional division of bandwidth.
> People also have been looking at extending block IO controller to provide
> throttling/max bandwidth control.
>
> I have started to write the support for throttling in block layer on
> request queue so that it can be used both for higher level logical
> devices as well as leaf nodes. This patch is still work in progress but
> I wanted to post it for early feedback.
>
> Basically currently I have hooked into __generic_make_request() function to
> check which cgroup bio belongs to and if it is exceeding the specified
> BW rate. If no, thread can continue to dispatch bio as it is otherwise
> bio is queued internally and dispatched later with the help of a worker
> thread.
>
> One can do bio throttling in terms of bandwidth(bytes per second) or in
> terms of IO per second or both. Both BW and IOPS rules can be put either
> on READ or WRITE flow.
>
> Throttling logic is independent of IO scheduler hence can be used with any
> IO scheduler operating. It also can be activated and used on any block
> device/request queue, in the stack.
>
> HOWTO
> =====
> - Make sure CONFIG_BLK_CGROUP=y and CONFIG_BLK_DEV_THROTTLING=y.
>
> - Mount blkio controller
>        mount -t cgroup -o blkio none /cgroup/blkio
>
> - Specify a bandwidth rate on particular device for root group. The format
>  for policy is "<major>:<minor>  <byes_per_second>".
>
>        echo "8:16  1048576" > /cgroup/blkio/blkio.throttle.read_bps_device
>
>  Above will put a limit of 1MB/second on reads happening for root group
>  on device having major/minor number 8:16.
>
> - Run dd to read a file and see if rate is throttled to 1MB/s or not.
>
>        # dd if=/mnt/common/zerofile of=/dev/null bs=4K count=1024 iflag=direct
>        1024+0 records in
>        1024+0 records out
>        4194304 bytes (4.2 MB) copied, 4.0001 s, 1.0 MB/s
>
> Note:
> -----
> - Limits for writes can be put using blkio.throttle.write_bps_device file.
> - Limits for IOPS rules can be put using following files.
>
>        blkio.throttle.read_iops_device
>        blkio.throttle.write_iops_device
>
>  Fore more info refer to Documentation/cgroup/blkio-controller.txt
>
> Open Issues
> ===========
> - Do we need to provide additional queue congestion semantics as we are
>  throttling and queuing bios at request queue and probably we don't want
>  a user space application to consume all the memory allocating bios
>  and bombarding request queue with those bios.
>
> TODO
> ====
> - Testing, bug fixes.
>
> Any feedback is welcome.
>
> Overall diffstat.
>
>  Documentation/cgroups/blkio-controller.txt |  106 +++-
>  block/Kconfig                              |   12 +
>  block/Makefile                             |    1 +
>  block/blk-cgroup.c                         |  786 ++++++++++++++++++-----
>  block/blk-cgroup.h                         |   79 +++-
>  block/blk-core.c                           |   24 +
>  block/blk-throttle.c                       |  999 ++++++++++++++++++++++++++++
>  block/cfq-iosched.c                        |    1 +
>  block/cfq.h                                |    2 +-
>  include/linux/blk_types.h                  |    3 +
>  include/linux/blkdev.h                     |   24 +
>  init/Kconfig                               |    9 +-
>  12 files changed, 1881 insertions(+), 165 deletions(-)
>
> Thanks
> Vivek
>
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