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

[Steven Pratt]

Nick Piggin wrote:

> 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.

Looks like Andrew beat you to it.  Both 2.5.70-mm7 and mm8 are back up 
to the previous performance levels for random reads.

Steve