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

From: Nick Piggin (
Date: Tue Jun 10 2003 - 20:00:40 EST

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.

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