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Performance regression between 2.6.32 and 2.6.38

To: "xfs@xxxxxxxxxxx" <xfs@xxxxxxxxxxx>
Subject: Performance regression between 2.6.32 and 2.6.38
From: Joshua Aune <luken@xxxxxxxxxxxx>
Date: Fri, 9 Sep 2011 18:23:54 -0600
Accept-language: en-US
Acceptlanguage: en-US
Cc: Paul Saab <ps@xxxxxx>
Thread-index: AcxvT+2VX2CITLKmSyuvmz5ryCC0jw==
Thread-topic: Performance regression between 2.6.32 and 2.6.38

We have been doing some performance testing on a handful of kernels and are 
seeing a significant performance regression with lower number of outstanding 
I/Os somewhere between 2.6.32 and 2.6.38.  The test case shows a significant 
drop in random read IOPS (45k -> 8k) and a significantly dirtier latency 

We also tested against the raw block device and against ext4.  The performance 
profiles of those tests were fairly consistent between the .32 and 3.0 based 
kernels where most of the testing was done.

Also worth noting, the test case below has 24 thread with one I/O each (~24 
outstanding total).  We did do a small number of tests that used 4 threads with 
libaio and 64 I/Os each (~256 total outstanding) which showed performance 
across the various kernel versions to be fairly stable.

-- Results

   bw=731,107 KB/s
   lat (usec): min=149 , max=2465 , avg=523.58, stdev=106.68
   lat (usec): 250=0.01%, 500=48.93%, 750=48.30%, 1000=2.70%
   lat (msec): 2=0.07%, 4=0.01% (aka 3.0)
  bw=128,702 KB/s
  lat (usec): min=77 , max=147441 , avg=452.33, stdev=2773.88
  lat (usec): 100=0.01%, 250=61.30%, 500=37.59%, 750=0.01%, 1000=0.01%
  lat (msec): 2=0.05%, 4=0.04%, 10=0.30%, 20=0.33%, 50=0.30%
  lat (msec): 100=0.07%, 250=0.01%

-- Testing Configuration

Most testing was performed on various 2 socket intel x5600 class server systems 
using various models of ioDrive.  The results above are from a 160GB ioDrive 
with a 2.3.1 driver.

The fio benchmark tool was used for most of the testing, but another benchmark 
showed similar results.

-- Testing  Process

# load the ioDrive driver
modprobe iomemory-vs

# Reset the ioDrive back to a known state
fio-detach /dev/fct0
fio-format -y /dev/fct0
fio-attach /dev/fct0

# Setup XFS for testing and create the sample file
mkfs.xfs -i size=2048 /dev/fioa
mkdir -p /mnt/tmp
mount -t xfs /dev/fioa /mnt/tmp
dd if=/dev/zero of=/mnt/tmp/bigfile bs=1M oflag=direct count=$((10*1024))

# Run fio test
fio --direct=1 --rw=randread --bs=16k --numjobs=24 --runtime=60 
--group_reporting --norandommap --time_based --ioengine=sync --name=file1 

-- Other

Are there any mount options or other tests that can be run in the failing 
configuration that would be helpful to isolate this further?


Please cc Paul and I, we are not subscribed to the list.

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