Re: 2.5.70-mm2 causes performance drop of random read O_DIRECT

[Nick Piggin <piggin@cyberone.com.au>]

Steven Pratt wrote:

> Nick Piggin wrote:
>
>> Steven Pratt wrote:
>>
>>> Starting in 2.5.70-mm2 and continuing in the mm tree, there is a 
>>> significant degrade in random read for block devices using 
>>> O_DIRECT.   The drop occurs for all block sizes and ranges from 
>>> 30%-40.  CPU usage is also lower although it may already be so low 
>>> as to be irrelavent.
>>
>>
>> Hi Steven, this is quite likely to be an io scheduler problem.
>> Is your test program rawread v2.1.5?
>
>
> This test was actually using 2.1.4, but the only difference in the 
> 2.1.5 version is a fix for the test label array for the aio versions 
> of the test.  No functional change, just fixed the outputed test 
> description.
>
>> What is the command line you are using to invoke the program? 
>
>
> rawread -t6 -p8 -m1 -d2 -s4096 -n65536 -l1 -z -x
>
> Which you can find if you follow either results link and look in the 
> benchmark directory where all raw benchmark out put is stored.
>

OK thanks, I can now reproduce this! I'll work on it.