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

[Balbir Singh]

* 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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