Re: [PATCH 0/9] cgroup: io-throttle controller (v13)

[Andrea Righi <righi.andrea@gmail.com>]

On Thu, Apr 30, 2009 at 09:20:58AM -0400, Alan D. Brunelle wrote:
> Hi Andrea -

Hi Alan,

> 
> FYI: I ran a simple test using this code to try and gauge the overhead
> incurred by enabling this technology. Using a single 400GB volume split
> into two 200GB partitions I ran two processes in parallel performing a
> mkfs (ext2) on each partition. First w/out cgroup io-throttle and then
> with it enabled (with each task having throttling enabled to
> 400MB/second (much, much more than the device is actually capable of
> doing)). The idea here is to see the base overhead of just having the
> io-throttle code in the paths.

Interesting. I've never explicitly measured the actual overhead of the
io-throttle infrastructure, I'll add a similar test to the io-throttle
testcase.

> 
> Doing 30 runs of each (w/out & w/ io-throttle enabled) shows very little
> difference (time in seconds)
> 
> w/out: min=80.196 avg=80.585 max=81.030 sdev=0.215 spread=0.834
> with:  min=80.402 avg=80.836 max=81.623 sdev=0.327 spread=1.221
> 
> So only around 0.3% overhead - and that may not be conclusive with the
> standard deviations seen.

You should see less overhead with reads respect to a pure write
workload, because with reads we don't need to check if the IO request
occurs in a different IO context. And things should be improved with
v16-rc1
(http://download.systemimager.org/~arighi/linux/patches/io-throttle/cgroup-io-throttle-v16-rc1.patch).

So, it would be also interesting to analyse the overhead of a read
stream compared to a write stream, as well a comparison of random
reads/writes. I'll do that in my next benchmarking session.

> 
> --
> 
> FYI: The test was run on 2.6.30-rc1+your patches on a 16-way x86_64 box
> (128GB RAM) plus a single FC volume off of a 1Gb FC RAID controller.
> 
> Regards,
> Alan D. Brunelle
> Hewlett-Packard

Thanks for posting these results,
-Andrea