Messages in this thread | | | Subject | Re: CFQ read performance regression | From | Miklos Szeredi <> | Date | Wed, 21 Apr 2010 18:05:11 +0200 |
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Jens, Corrado,
Here's a graph showing the number of issued but not yet completed requests versus time for CFQ and NOOP schedulers running the tiobench benchmark with 8 threads:
http://www.kernel.org/pub/linux/kernel/people/mszeredi/blktrace/queue-depth.jpg
It shows pretty clearly the performance problem is because CFQ is not issuing enough request to fill the bandwidth.
Is this the correct behavior of CFQ or is this a bug?
This is on a vanilla 2.6.34-rc4 kernel with two tunables modified:
read_ahead_kb=512 low_latency=0 (for CFQ)
Thanks, Miklos
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