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

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.

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