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 -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
