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