Re: IO scheduler benchmarking

[Andrew Morton <akpm@digeo.com>]

David Lang <david.lang@digitalinsight.com> wrote:
>
> one other useful test would be the time to copy a large (multi-gig) file.
> currently this takes forever and uses very little fo the disk bandwidth, I
> suspect that the AS would give more preference to reads and therefor would
> go faster.

Yes, that's a test.

	time (cp 1-gig-file foo ; sync)

2.5.62-mm2,AS:		1:22.36
2.5.62-mm2,CFQ:		1:25.54
2.5.62-mm2,deadline:	1:11.03
2.4.21-pre4:		1:07.69

Well gee.


> for a real-world example, mozilla downloads files to a temp directory and
> then copies it to the premanent location. When I download a video from my
> tivo it takes ~20 min to download a 1G video, during which time the system
> is perfectly responsive, then after the download completes when mozilla
> copies it to the real destination (on a seperate disk so it is a copy, not
> just a move) the system becomes completely unresponsive to anything
> requireing disk IO for several min.

Well 2.4 is unreponsive period.  That's due to problems in the VM - processes
which are trying to allocate memory get continually DoS'ed by `cp' in page
reclaim.

For the reads-starved-by-writes problem which you describe, you'll see that
quite a few of the tests did cover that.  contest does as well.