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:
>>
>>> 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.
>

No, that was me ;)
Odd, I was still seeing a regression with mm7, but thats
fixed in mm8. Thanks for testing.