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    SubjectRe: [RFC] IO scheduler based IO controller V7
    Vivek Goyal wrote:
    > On Fri, Jul 31, 2009 at 01:21:51PM +0800, Gui Jianfeng wrote:
    >> Hi Vivek,
    >>
    >> Here are some test results for normal reads and write for IO Controller V7 by fio.
    >> Tested with "fairness == 0". It seems performance gets better comparing with V6.
    >>
    >> Mode Normal read | Random read | Normal write | Random write | Direct read | Direct Write
    >>
    >> 2.6.31-rc1 71,613KiB/s 3,606KiB/s 66,250KiB/s 9,420KiB/s 51,535KiB/s 55,752KiB/s
    >>
    >> V7 70,540KiB/s 3,551KiB/s 64,548KiB/s 9,677KiB/s 53,530KiB/s 54,145KiB/s
    >>
    >> Performance -1.5% -1.5% -2.6% +2.7% +3.9% -2.9%
    >>
    >
    > Thanks Gui. Can you also try V7 with CONFIG_TRACK_ASYNC_CONTEXT=n. I tried
    > that and I got better results for buffered writes.

    Yes, I'm also going to try it.

    >
    > In my testing I still see some performance regression for buffered writes
    > which goes away if I disable group io scheduling and just use flat mode.
    >
    > I will spend more time to find out where it is coming from.
    >
    > Thanks
    > Vivek
    >
    >
    >> Vivek Goyal wrote:
    >>> Hi All,
    >>>
    >>> Here is the V7 of the IO controller patches generated on top of 2.6.31-rc4.
    >>>
    >>> For ease of patching, a consolidated patch is available here.
    >>>
    >>> http://people.redhat.com/~vgoyal/io-controller/io-scheduler-based-io-controller-v7.patch
    >>>
    >>> Previous versions of the patches was posted here.
    >>>
    >>> (V1) http://lkml.org/lkml/2009/3/11/486
    >>> (V2) http://lkml.org/lkml/2009/5/5/275
    >>> (V3) http://lkml.org/lkml/2009/5/26/472
    >>> (V4) http://lkml.org/lkml/2009/6/8/580
    >>> (V5) http://lkml.org/lkml/2009/6/19/279
    >>> (V6) http://lkml.org/lkml/2009/7/2/369
    >>>
    >>> Changes from V6
    >>> ===============
    >>> - Introduced the notion of group_idling where we idle for next request to
    >>> come from the same group before we expire it. It is along the lines of
    >>> cfq's slice_idle thing to provide fairness. Switching to group idling
    >>> now helps in the sense that we don't have to rely whether queue idling
    >>> was turned on or not by CFQ. It becomes too much of debugging pain with
    >>> different work loads and different kind of storage media. Introduction
    >>> of group_idle should help.
    >>>
    >>> - Moved some of the code like dynamic queue idling update, arming queue
    >>> idling timer, keeping track of average think time etc back to CFQ. With
    >>> group idling we don't need it now. Reduce the amount of change.
    >>>
    >>> - Enabled cfq's close cooperator functionality in groups. So far this worked
    >>> only in root group. Now it should work in non-root groups also.
    >>>
    >>> - Got rid of the patch where we calculated disk time based on average disk
    >>> rate in some circumstances. It was giving bad numbers in early queue
    >>> deletion cases. Also did not think that it was helping a lot. Remvoed it
    >>> for the time being.
    >>>
    >>> - Added an experimental patch to map sync requests using bio tracking info and
    >>> not task context. This is only for noop, deadline and AS.
    >>>
    >>> - Got rid of experimental patch of idling for async queues. Don't think it
    >>> was helping.
    >>>
    >>> - Got rid of wait_busy and wait_busy_done logic from queue. Instead
    >>> implemented it for groups.
    >>>
    >>> - Introduced oom_ioq to accomodate oom_cfqq change recently.
    >>>
    >>> - Broke-up elv_init_ioq() fn into smaller functions. It had 7 arguments and
    >>> looked complicated.
    >>>
    >>> - Fixed a bug in blk_queue_io_group_congested(). Thanks to Munehiro Ikeda.
    >>>
    >>> - Merged gui's patch to fix the cgroup file format issue.
    >>>
    >>> - Merged gui's patch to update per group congestion limit when
    >>> q->nr_group_requests is updated.
    >>>
    >>> - Fixed a bug where close cooperation will not work if we wait for all the
    >>> requests to finish from previous queue.
    >>>
    >>> - Fixed group deletion accouting where deletion from idle tree were also
    >>> appearing in the log.
    >>>
    >>> - Got rid of busy_rt_queues infrastructure.
    >>>
    >>> - Got rid of elv_ioq_request_dispatched(). An helper function just to
    >>> increment a variable.
    >>>
    >>> Limitations
    >>> ===========
    >>>
    >>> - This IO controller provides the bandwidth control at the IO scheduler
    >>> level (leaf node in stacked hiearchy of logical devices). So there can
    >>> be cases (depending on configuration) where application does not see
    >>> proportional BW division at higher logical level device.
    >>>
    >>> LWN has written an article about the issue here.
    >>>
    >>> http://lwn.net/Articles/332839/
    >>>
    >>> How to solve the issue of fairness at higher level logical devices
    >>> ==================================================================
    >>> (Do we really need it? That's not where the contention for resources is.)
    >>>
    >>> Couple of suggestions have come forward.
    >>>
    >>> - Implement IO control at IO scheduler layer and then with the help of
    >>> some daemon, adjust the weight on underlying devices dynamiclly, depending
    >>> on what kind of BW gurantees are to be achieved at higher level logical
    >>> block devices.
    >>>
    >>> - Also implement a higher level IO controller along with IO scheduler
    >>> based controller and let user choose one depending on his needs.
    >>>
    >>> A higher level controller does not know about the assumptions/policies
    >>> of unerldying IO scheduler, hence it has the potential to break down
    >>> the IO scheduler's policy with-in cgroup. A lower level controller
    >>> can work with IO scheduler much more closely and efficiently.
    >>>
    >>> Other active IO controller developments
    >>> =======================================
    >>>
    >>> IO throttling
    >>> -------------
    >>>
    >>> This is a max bandwidth controller and not the proportional one. Secondly
    >>> it is a second level controller which can break the IO scheduler's
    >>> policy/assumtions with-in cgroup.
    >>>
    >>> dm-ioband
    >>> ---------
    >>>
    >>> This is a proportional bandwidth controller implemented as device mapper
    >>> driver. It is also a second level controller which can break the
    >>> IO scheduler's policy/assumptions with-in cgroup.
    >>>
    >>> TODO
    >>> ====
    >>> - code cleanups, testing, bug fixing, optimizations, benchmarking etc...
    >>>
    >>> Testing
    >>> =======
    >>>
    >>> I have been able to do some testing as follows. All my testing is with ext3
    >>> file system with a SATA drive which supports queue depth of 31.
    >>>
    >>> Test1 (Isolation between two KVM virtual machines)
    >>> ==================================================
    >>> Created two KVM virtual machines. Partitioned a disk on host in two partitions
    >>> and gave one partition to each virtual machine. Put both the virtual machines
    >>> in two different cgroup of weight 1000 and 500 each. Virtual machines created
    >>> ext3 file system on the partitions exported from host and did buffered writes.
    >>> Host seems writes as synchronous and virtual machine with higher weight gets
    >>> double the disk time of virtual machine of lower weight. Used deadline
    >>> scheduler in this test case.
    >>>
    >>> Some more details about configuration are in documentation patch.
    >>>
    >>> Test2 (Fairness for synchronous reads)
    >>> ======================================
    >>> - Two dd in two cgroups with cgrop weights 1000 and 500. Ran two "dd" in those
    >>> cgroups (With CFQ scheduler and /sys/block/<device>/queue/fairness = 1)
    >>>
    >>> Higher weight dd finishes first and at that point of time my script takes
    >>> care of reading cgroup files io.disk_time and io.disk_sectors for both the
    >>> groups and display the results.
    >>>
    >>> dd if=/mnt/$BLOCKDEV/zerofile1 of=/dev/null &
    >>> dd if=/mnt/$BLOCKDEV/zerofile2 of=/dev/null &
    >>>
    >>> 234179072 bytes (234 MB) copied, 3.9065 s, 59.9 MB/s
    >>> 234179072 bytes (234 MB) copied, 5.19232 s, 45.1 MB/s
    >>>
    >>> group1 time=8 16 2471 group1 sectors=8 16 457840
    >>> group2 time=8 16 1220 group2 sectors=8 16 225736
    >>>
    >>> First two fields in time and sectors statistics represent major and minor
    >>> number of the device. Third field represents disk time in milliseconds and
    >>> number of sectors transferred respectively.
    >>>
    >>> This patchset tries to provide fairness in terms of disk time received. group1
    >>> got almost double of group2 disk time (At the time of first dd finish). These
    >>> time and sectors statistics can be read using io.disk_time and io.disk_sector
    >>> files in cgroup. More about it in documentation file.
    >>>
    >>> Test3 (Reader Vs Buffered Writes)
    >>> ================================
    >>> Buffered writes can be problematic and can overwhelm readers, especially with
    >>> noop and deadline. IO controller can provide isolation between readers and
    >>> buffered (async) writers.
    >>>
    >>> First I ran the test without io controller to see the severity of the issue.
    >>> Ran a hostile writer and then after 10 seconds started a reader and then
    >>> monitored the completion time of reader. Reader reads a 256 MB file. Tested
    >>> this with noop scheduler.
    >>>
    >>> sample script
    >>> ------------
    >>> sync
    >>> echo 3 > /proc/sys/vm/drop_caches
    >>> time dd if=/dev/zero of=/mnt/sdb/reader-writer-zerofile bs=4K count=2097152
    >>> conv=fdatasync &
    >>> sleep 10
    >>> time dd if=/mnt/sdb/256M-file of=/dev/null &
    >>>
    >>> Results
    >>> -------
    >>> 8589934592 bytes (8.6 GB) copied, 106.045 s, 81.0 MB/s (Writer)
    >>> 268435456 bytes (268 MB) copied, 96.5237 s, 2.8 MB/s (Reader)
    >>>
    >>> Now it was time to test io controller whether it can provide isolation between
    >>> readers and writers with noop. I created two cgroups of weight 1000 each and
    >>> put reader in group1 and writer in group 2 and ran the test again. Upon
    >>> comletion of reader, my scripts read io.dis_time and io.disk_group cgroup
    >>> files to get an estimate how much disk time each group got and how many
    >>> sectors each group did IO for.
    >>>
    >>> For more accurate accounting of disk time for buffered writes with queuing
    >>> hardware I had to set /sys/block/<disk>/queue/iosched/fairness to "1".
    >>>
    >>> sample script
    >>> -------------
    >>> echo $$ > /cgroup/bfqio/test2/tasks
    >>> dd if=/dev/zero of=/mnt/$BLOCKDEV/testzerofile bs=4K count=2097152 &
    >>> sleep 10
    >>> echo noop > /sys/block/$BLOCKDEV/queue/scheduler
    >>> echo 1 > /sys/block/$BLOCKDEV/queue/iosched/fairness
    >>> echo $$ > /cgroup/bfqio/test1/tasks
    >>> dd if=/mnt/$BLOCKDEV/256M-file of=/dev/null &
    >>> wait $!
    >>> # Some code for reading cgroup files upon completion of reader.
    >>> -------------------------
    >>>
    >>> Results
    >>> =======
    >>> 268435456 bytes (268 MB) copied, 6.65819 s, 40.3 MB/s (Reader)
    >>>
    >>> group1 time=8 16 3063 group1 sectors=8 16 524808
    >>> group2 time=8 16 3071 group2 sectors=8 16 441752
    >>>
    >>> Note, reader finishes now much lesser time and both group1 and group2
    >>> got almost 3 seconds of disk time. Hence io-controller provides isolation
    >>> from buffered writes.
    >>>
    >>> Test4 (AIO)
    >>> ===========
    >>>
    >>> AIO reads
    >>> -----------
    >>> Set up two fio, AIO read jobs in two cgroup with weight 1000 and 500
    >>> respectively. I am using cfq scheduler. Following are some lines from my test
    >>> script.
    >>>
    >>> ---------------------------------------------------------------
    >>> echo 1000 > /cgroup/bfqio/test1/io.weight
    >>> echo 500 > /cgroup/bfqio/test2/io.weight
    >>>
    >>> fio_args="--ioengine=libaio --rw=read --size=512M --direct=1"
    >>> echo 1 > /sys/block/$BLOCKDEV/queue/iosched/fairness
    >>>
    >>> echo $$ > /cgroup/bfqio/test1/tasks
    >>> fio $fio_args --name=test1 --directory=/mnt/$BLOCKDEV/fio1/
    >>> --output=/mnt/$BLOCKDEV/fio1/test1.log
    >>> --exec_postrun="../read-and-display-group-stats.sh $maj_dev $minor_dev" &
    >>>
    >>> echo $$ > /cgroup/bfqio/test2/tasks
    >>> fio $fio_args --name=test2 --directory=/mnt/$BLOCKDEV/fio2/
    >>> --output=/mnt/$BLOCKDEV/fio2/test2.log &
    >>> ----------------------------------------------------------------
    >>>
    >>> test1 and test2 are two groups with weight 1000 and 500 respectively.
    >>> "read-and-display-group-stats.sh" is one small script which reads the
    >>> test1 and test2 cgroup files to determine how much disk time each group
    >>> got till first fio job finished.
    >>>
    >>> Results
    >>> ------
    >>> test1 statistics: time=8 16 22403 sectors=8 16 1049640
    >>> test2 statistics: time=8 16 11400 sectors=8 16 552864
    >>>
    >>> Above shows that by the time first fio (higher weight), finished, group
    >>> test1 got 22403 ms of disk time and group test2 got 11400 ms of disk time.
    >>> similarly the statistics for number of sectors transferred are also shown.
    >>>
    >>> Note that disk time given to group test1 is almost double of group2 disk
    >>> time.
    >>>
    >>> AIO writes
    >>> ----------
    >>> Set up two fio, AIO direct write jobs in two cgroup with weight 1000 and 500
    >>> respectively. I am using cfq scheduler. Following are some lines from my test
    >>> script.
    >>>
    >>> ------------------------------------------------
    >>> echo 1000 > /cgroup/bfqio/test1/io.weight
    >>> echo 500 > /cgroup/bfqio/test2/io.weight
    >>> fio_args="--ioengine=libaio --rw=write --size=512M --direct=1"
    >>>
    >>> echo 1 > /sys/block/$BLOCKDEV/queue/iosched/fairness
    >>>
    >>> echo $$ > /cgroup/bfqio/test1/tasks
    >>> fio $fio_args --name=test1 --directory=/mnt/$BLOCKDEV/fio1/
    >>> --output=/mnt/$BLOCKDEV/fio1/test1.log
    >>> --exec_postrun="../read-and-display-group-stats.sh $maj_dev $minor_dev" &
    >>>
    >>> echo $$ > /cgroup/bfqio/test2/tasks
    >>> fio $fio_args --name=test2 --directory=/mnt/$BLOCKDEV/fio2/
    >>> --output=/mnt/$BLOCKDEV/fio2/test2.log &
    >>> -------------------------------------------------
    >>>
    >>> test1 and test2 are two groups with weight 1000 and 500 respectively.
    >>> "read-and-display-group-stats.sh" is one small script which reads the
    >>> test1 and test2 cgroup files to determine how much disk time each group
    >>> got till first fio job finished.
    >>>
    >>> Following are the results.
    >>>
    >>> test1 statistics: time=8 16 29085 sectors=8 16 1049656
    >>> test2 statistics: time=8 16 14652 sectors=8 16 516728
    >>>
    >>> Above shows that by the time first fio (higher weight), finished, group
    >>> test1 got 28085 ms of disk time and group test2 got 14652 ms of disk time.
    >>> similarly the statistics for number of sectors transferred are also shown.
    >>>
    >>> Note that disk time given to group test1 is almost double of group2 disk
    >>> time.
    >>>
    >>> Test5 (Fairness for async writes, Buffered Write Vs Buffered Write)
    >>> ===================================================================
    >>> Fairness for async writes is tricky and biggest reason is that async writes
    >>> are cached in higher layers (page cahe) as well as possibly in file system
    >>> layer also (btrfs, xfs etc), and are dispatched to lower layers not necessarily
    >>> in proportional manner.
    >>>
    >>> For example, consider two dd threads reading /dev/zero as input file and doing
    >>> writes of huge files. Very soon we will cross vm_dirty_ratio and dd thread will
    >>> be forced to write out some pages to disk before more pages can be dirtied. But
    >>> not necessarily dirty pages of same thread are picked. It can very well pick
    >>> the inode of lesser priority dd thread and do some writeout. So effectively
    >>> higher weight dd is doing writeouts of lower weight dd pages and we don't see
    >>> service differentation.
    >>>
    >>> IOW, the core problem with async write fairness is that higher weight thread
    >>> does not throw enought IO traffic at IO controller to keep the queue
    >>> continuously backlogged. In my testing, there are many .2 to .8 second
    >>> intervals where higher weight queue is empty and in that duration lower weight
    >>> queue get lots of job done giving the impression that there was no service
    >>> differentiation.
    >>>
    >>> In summary, from IO controller point of view async writes support is there.
    >>> Because page cache has not been designed in such a manner that higher
    >>> prio/weight writer can do more write out as compared to lower prio/weight
    >>> writer, gettting service differentiation is hard and it is visible in some
    >>> cases and not visible in some cases.
    >>>
    >>> Do we really care that much for fairness among two writer cgroups? One can
    >>> choose to do direct writes or sync writes if fairness for writes really
    >>> matters for him.
    >>>
    >>> Following is the only case where it is hard to ensure fairness between cgroups.
    >>>
    >>> - Buffered writes Vs Buffered Writes.
    >>>
    >>> So to test async writes I created two partitions on a disk and created ext3
    >>> file systems on both the partitions. Also created two cgroups and generated
    >>> lots of write traffic in two cgroups (50 fio threads) and watched the disk
    >>> time statistics in respective cgroups at the interval of 2 seconds. Thanks to
    >>> ryo tsuruta for the test case.
    >>>
    >>> *****************************************************************
    >>> sync
    >>> echo 3 > /proc/sys/vm/drop_caches
    >>>
    >>> fio_args="--size=64m --rw=write --numjobs=50 --group_reporting"
    >>>
    >>> echo $$ > /cgroup/bfqio/test1/tasks
    >>> fio $fio_args --name=test1 --directory=/mnt/sdd1/fio/ --output=/mnt/sdd1/fio/test1.log &
    >>>
    >>> echo $$ > /cgroup/bfqio/test2/tasks
    >>> fio $fio_args --name=test2 --directory=/mnt/sdd2/fio/ --output=/mnt/sdd2/fio/test2.log &
    >>> ***********************************************************************
    >>>
    >>> And watched the disk time and sector statistics for the both the cgroups
    >>> every 2 seconds using a script. How is snippet from output.
    >>>
    >>> test1 statistics: time=8 48 1315 sectors=8 48 55776 dq=8 48 1
    >>> test2 statistics: time=8 48 633 sectors=8 48 14720 dq=8 48 2
    >>>
    >>> test1 statistics: time=8 48 5586 sectors=8 48 339064 dq=8 48 2
    >>> test2 statistics: time=8 48 2985 sectors=8 48 146656 dq=8 48 3
    >>>
    >>> test1 statistics: time=8 48 9935 sectors=8 48 628728 dq=8 48 3
    >>> test2 statistics: time=8 48 5265 sectors=8 48 278688 dq=8 48 4
    >>>
    >>> test1 statistics: time=8 48 14156 sectors=8 48 932488 dq=8 48 6
    >>> test2 statistics: time=8 48 7646 sectors=8 48 412704 dq=8 48 7
    >>>
    >>> test1 statistics: time=8 48 18141 sectors=8 48 1231488 dq=8 48 10
    >>> test2 statistics: time=8 48 9820 sectors=8 48 548400 dq=8 48 8
    >>>
    >>> test1 statistics: time=8 48 21953 sectors=8 48 1485632 dq=8 48 13
    >>> test2 statistics: time=8 48 12394 sectors=8 48 698288 dq=8 48 10
    >>>
    >>> test1 statistics: time=8 48 25167 sectors=8 48 1705264 dq=8 48 13
    >>> test2 statistics: time=8 48 14042 sectors=8 48 817808 dq=8 48 10
    >>>
    >>> First two fields in time and sectors statistics represent major and minor
    >>> number of the device. Third field represents disk time in milliseconds and
    >>> number of sectors transferred respectively.
    >>>
    >>> So disk time consumed by group1 is almost double of group2 in this case.
    >>>
    >>> Your feedback is welcome.
    >>>
    >>> Thanks
    >>> Vivek
    >>>
    >>>
    >>>
    >> --
    >> Regards
    >> Gui Jianfeng
    >
    >
    >

    --
    Regards
    Gui Jianfeng



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