Re: [RFC] [PATCH v2 0/8] Provide cgroup isolation for bufferedwrites.

From: Balbir Singh
Date: Fri Mar 25 2011 - 03:47:06 EST


* Justin TerAvest <teravest@xxxxxxxxxx> [2011-03-22 16:08:47]:

> This patchset adds tracking to the page_cgroup structure for which cgroup has
> dirtied a page, and uses that information to provide isolation between
> cgroups performing writeback.
>
> I know that there is some discussion to remove request descriptor limits
> entirely, but I included a patch to introduce per-cgroup limits to enable
> this functionality. Without it, we didn't see much isolation improvement.
>
> I think most of this material has been discussed on lkml previously, this is
> just another attempt to make a patchset that handles buffered writes for CFQ.
>
> There was a lot of previous discussion at:
> http://thread.gmane.org/gmane.linux.kernel/1007922
>
> Thanks to Andrea Righi, Kamezawa Hiroyuki, Munehiro Ikeda, Nauman Rafique,
> and Vivek Goyal for work on previous versions of these patches.
>
> For version 2:
> - I collected more statistics and provided data in the cover sheet
> - blkio id is now stored inside "flags" in page_cgroup, with cmpxchg
> - I cleaned up some patch names
> - Added symmetric reference wrappers in cfq-iosched
>
> There are a couple lingering issues that exist in this patchset-- it's meant
> to be an RFC to discuss the overall design for tracking of buffered writes.
> I have at least a couple of patches to finish to make absolutely sure that
> refcounts and locking are handled properly, I just need to do more testing.
>
> Documentation/block/biodoc.txt | 10 +
> block/blk-cgroup.c | 203 +++++++++++++++++-
> block/blk-cgroup.h | 9 +-
> block/blk-core.c | 218 +++++++++++++------
> block/blk-settings.c | 2 +-
> block/blk-sysfs.c | 59 +++---
> block/cfq-iosched.c | 473 ++++++++++++++++++++++++++++++----------
> block/cfq.h | 6 +-
> block/elevator.c | 7 +-
> fs/buffer.c | 2 +
> fs/direct-io.c | 2 +
> include/linux/blk_types.h | 2 +
> include/linux/blkdev.h | 81 +++++++-
> include/linux/blkio-track.h | 89 ++++++++
> include/linux/elevator.h | 14 +-
> include/linux/iocontext.h | 1 +
> include/linux/memcontrol.h | 6 +
> include/linux/mmzone.h | 4 +-
> include/linux/page_cgroup.h | 38 +++-
> init/Kconfig | 16 ++
> mm/Makefile | 3 +-
> mm/bounce.c | 2 +
> mm/filemap.c | 2 +
> mm/memcontrol.c | 6 +
> mm/memory.c | 6 +
> mm/page-writeback.c | 14 +-
> mm/page_cgroup.c | 29 ++-
> mm/swap_state.c | 2 +
> 28 files changed, 1066 insertions(+), 240 deletions(-)
>
>
> 8f0b0f4 cfq: Don't allow preemption across cgroups
> a47cdc6 block: Per cgroup request descriptor counts
> 8dd7adb cfq: add per cgroup writeout done by flusher stat
> 1fa0b6d cfq: Fix up tracked async workload length.
> e9e85d3 block: Modify CFQ to use IO tracking information.
> f8ffb19 cfq-iosched: Make async queues per cgroup
> 1d9ee09 block,fs,mm: IO cgroup tracking for buffered write
> 31c7321 cfq-iosched: add symmetric reference wrappers
>
>
> ===================================== Isolation experiment results
>
> For isolation testing, we run a test that's available at:
> git://google3-2.osuosl.org/tests/blkcgroup.git
>
> It creates containers, runs workloads, and checks to see how well we meet
> isolation targets. For the purposes of this patchset, I only ran
> tests among buffered writers.
>
> Before patches
> ==============
> 10:32:06 INFO experiment 0 achieved DTFs: 666, 333
> 10:32:06 INFO experiment 0 FAILED: max observed error is 167, allowed is 150
> 10:32:51 INFO experiment 1 achieved DTFs: 647, 352
> 10:32:51 INFO experiment 1 FAILED: max observed error is 253, allowed is 150
> 10:33:35 INFO experiment 2 achieved DTFs: 298, 701
> 10:33:35 INFO experiment 2 FAILED: max observed error is 199, allowed is 150
> 10:34:19 INFO experiment 3 achieved DTFs: 445, 277, 277
> 10:34:19 INFO experiment 3 FAILED: max observed error is 155, allowed is 150
> 10:35:05 INFO experiment 4 achieved DTFs: 418, 104, 261, 215
> 10:35:05 INFO experiment 4 FAILED: max observed error is 232, allowed is 150
> 10:35:53 INFO experiment 5 achieved DTFs: 213, 136, 68, 102, 170, 136, 170
> 10:35:53 INFO experiment 5 PASSED: max observed error is 73, allowed is 150
> 10:36:04 INFO -----ran 6 experiments, 1 passed, 5 failed
>
> After patches
> =============
> 11:05:22 INFO experiment 0 achieved DTFs: 501, 498
> 11:05:22 INFO experiment 0 PASSED: max observed error is 2, allowed is 150
> 11:06:07 INFO experiment 1 achieved DTFs: 874, 125
> 11:06:07 INFO experiment 1 PASSED: max observed error is 26, allowed is 150
> 11:06:53 INFO experiment 2 achieved DTFs: 121, 878
> 11:06:53 INFO experiment 2 PASSED: max observed error is 22, allowed is 150
> 11:07:46 INFO experiment 3 achieved DTFs: 589, 205, 204
> 11:07:46 INFO experiment 3 PASSED: max observed error is 11, allowed is 150
> 11:08:34 INFO experiment 4 achieved DTFs: 616, 109, 109, 163
> 11:08:34 INFO experiment 4 PASSED: max observed error is 34, allowed is 150
> 11:09:29 INFO experiment 5 achieved DTFs: 139, 139, 139, 139, 140, 141, 160
> 11:09:29 INFO experiment 5 PASSED: max observed error is 1, allowed is 150
> 11:09:46 INFO -----ran 6 experiments, 6 passed, 0 failed

Could you explain what max observed errors is all about?

>
> Summary
> =======
> Isolation between buffered writers is clearly better with this patch.
>
>
> =============================== Read latency results
> To test read latency, I created two containers:
> - One called "readers", with weight 900
> - One called "writers", with weight 100
>
> I ran this fio workload in "readers":
> [global]
> directory=/mnt/iostestmnt/fio
> runtime=30
> time_based=1
> group_reporting=1
> exec_prerun='echo 3 > /proc/sys/vm/drop_caches'

Is this sufficient, do you need a sync prior to this?

> cgroup_nodelete=1
> bs=4K
> size=512M
>
> [iostest-read]
> description="reader"
> numjobs=16
> rw=randread
> new_group=1
>
>
> ....and this fio workload in "writers"
> [global]
> directory=/mnt/iostestmnt/fio
> runtime=30
> time_based=1
> group_reporting=1
> exec_prerun='echo 3 > /proc/sys/vm/drop_caches'
> cgroup_nodelete=1
> bs=4K
> size=512M
>
> [iostest-write]
> description="writer"
> cgroup=writers
> numjobs=3
> rw=write
> new_group=1
>
>
>
> I've pasted the results from the "read" workload inline.
>
> Before patches
> ==============
> Starting 16 processes
>
> Jobs: 14 (f=14): [_rrrrrr_rrrrrrrr] [36.2% done] [352K/0K /s] [86 /0 iops] [eta 01m:00s]·············
> iostest-read: (groupid=0, jobs=16): err= 0: pid=20606
> Description : ["reader"]
> read : io=13532KB, bw=455814 B/s, iops=111 , runt= 30400msec
> clat (usec): min=2190 , max=30399K, avg=30395175.13, stdev= 0.20
> lat (usec): min=2190 , max=30399K, avg=30395177.07, stdev= 0.20
> bw (KB/s) : min= 0, max= 260, per=0.00%, avg= 0.00, stdev= 0.00
> cpu : usr=0.00%, sys=0.03%, ctx=3691, majf=2, minf=468
> IO depths : 1=100.0%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, >=64=0.0%
> submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
> complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
> issued r/w/d: total=3383/0/0, short=0/0/0
>
> lat (msec): 4=0.03%, 10=2.66%, 20=74.84%, 50=21.90%, 100=0.09%
> lat (msec): 250=0.06%, >=2000=0.41%
>
> Run status group 0 (all jobs):
> READ: io=13532KB, aggrb=445KB/s, minb=455KB/s, maxb=455KB/s, mint=30400msec, maxt=30400msec
>
> Disk stats (read/write):
> sdb: ios=3744/18, merge=0/16, ticks=542713/1675, in_queue=550714, util=99.15%
>
>
>
> After patches
> =============
> tarting 16 processes
> Jobs: 16 (f=16): [rrrrrrrrrrrrrrrr] [100.0% done] [557K/0K /s] [136 /0 iops] [eta 00m:00s]
> iostest-read: (groupid=0, jobs=16): err= 0: pid=14183
> Description : ["reader"]
> read : io=14940KB, bw=506105 B/s, iops=123 , runt= 30228msec
> clat (msec): min=2 , max=29866 , avg=463.42, stdev=101.84
> lat (msec): min=2 , max=29866 , avg=463.42, stdev=101.84
> bw (KB/s) : min= 0, max= 198, per=31.69%, avg=156.52, stdev=17.83
> cpu : usr=0.01%, sys=0.03%, ctx=4274, majf=2, minf=464
> IO depths : 1=100.0%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, >=64=0.0%
> submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
> complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
> issued r/w/d: total=3735/0/0, short=0/0/0
>
> lat (msec): 4=0.05%, 10=0.32%, 20=32.99%, 50=64.61%, 100=1.26%
> lat (msec): 250=0.11%, 500=0.11%, 750=0.16%, 1000=0.05%, >=2000=0.35%
>
> Run status group 0 (all jobs):
> READ: io=14940KB, aggrb=494KB/s, minb=506KB/s, maxb=506KB/s, mint=30228msec, maxt=30228msec
>
> Disk stats (read/write):
> sdb: ios=4189/0, merge=0/0, ticks=96428/0, in_queue=478798, util=100.00%
>

This shows an improvement in read b/w, what does the writer
output look like?

--
Three Cheers,
Balbir
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