On 7/1/12 4:01 PM, Stefan Priebe wrote:
Hello list,
Hello sage,
i've made some further tests.
Sequential 4k writes over 200GB: 300% CPU usage of kvm process 34712 iops
Random 4k writes over 200GB: 170% CPU usage of kvm process 5500 iops
When i make random 4k writes over 100MB: 450% CPU usage of kvm process
and !! 25059 iops !!
When you say 100MB vs 200GB, do you mean the total amount of data that
is written for the test? Also, are these starting out on a fresh
filesystem? Recently I've been working on tracking down an issue where
small write performance is degrading as data is written. The tests I've
done have been for sequential writes, but I wonder if the problem may be
significantly worse with random writes.
Random 4k writes over 1GB: 380% CPU usage of kvm process 14387 iops
So the range where the random I/O happen seem to be important and the
cpu usage just seem to reflect the iops.
So i'm not sure if the problem is really the client rbd driver. Mark i
hope you can make some tests next week.
I need to get perf setup on our test boxes, but once I do that I'm
hoping to follow up on this.
Greets
Stefan
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Mark
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