Re: CFQ read performance regression
From: Miklos Szeredi
Date: Wed Apr 21 2010 - 12:05:19 EST
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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