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

From: Steven Pratt (
Date: Wed Jun 11 2003 - 10:16:13 EST

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.


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