linux-kernel - cfq performance gap

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Date:	Thu, 07 Dec 2006 16:03:20 -0800
From:	Avantika Mathur <mathur@...ibm.com>
To:	axboe@...e.de
Cc:	linux-kernel@...r.kernel.org
Subject: cfq performance gap

Hi Jens, 

I've noticed a performance gap between the cfq scheduler and other io
schedulers when running the rawio benchmark. 
Results from rawio on 2.6.19, cfq and noop schedulers: 

CFQ: 

procs           device    num read   KB/sec     I/O Ops/sec 
-----  ---------------  ----------  -------  -------------- 
  16         /dev/sda       16412     8338            2084 
-----  ---------------  ----------  -------  -------------- 
  16                        16412     8338            2084 

Total run time 0.492072 seconds 


NOOP: 

procs           device    num read   KB/sec     I/O Ops/sec 
-----  ---------------  ----------  -------  -------------- 
  16         /dev/sda       16399    29224            7306 
-----  ---------------  ----------  -------  -------------- 
  16                        16399    29224            7306 

Total run time 0.140284 seconds 

The benchmark workload is 16 processes running 4k random reads. 

Is this performance gap a known issue? 
Thanks, 
Avantika Mathur 


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