Re: [RFC PATCH] cfq-iosched: IOPS mode for group scheduling and newgroup_idle tunable

[Christoph Hellwig]

On Wed, Jul 28, 2010 at 04:22:12PM -0400, Vivek Goyal wrote:
> I also did "time firefox &" testing to see how long firefox takes to
> launch when linus torture test is running and without patch it took
> around 20 seconds and with patch it took around 17 seconds. 
> 
> So to me above test results suggest that this patch does not worsen
> the performance. In fact it helps. (at least on ext3 file system.)
> 
> Not sure why are you seeing different results with XFS.

So why didn't you test it with XFS to verify his results?  We all know
that different filesystems have different I/O patters, and we have
a history of really nasty regressions in one filesystem by good meaning
changes to the I/O scheduler.

ext3 in fact is a particularly bad test case as it not only doesn't have
I/O barriers enabled, but also has particularly bad I/O patterns
compared to modern filesystems.

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