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SubjectRe: IO scheduler benchmarking
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.

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.

David Lang

On Thu, 20 Feb 2003, Andrew Morton wrote:

> Date: Thu, 20 Feb 2003 21:23:04 -0800
> From: Andrew Morton <>
> To:
> Subject: IO scheduler benchmarking
> Following this email are the results of a number of tests of various I/O
> schedulers:
> - Anticipatory Scheduler (AS) (from 2.5.61-mm1 approx)
> - CFQ (as in 2.5.61-mm1)
> - 2.5.61+hacks (Basically 2.5.61 plus everything before the anticipatory
> scheduler - tweaks which fix the writes-starve-reads problem via a
> scheduling storm)
> - 2.4.21-pre4
> All these tests are simple things from the command line.
> I stayed away from the standard benchmarks because they do not really touch
> on areas where the Linux I/O scheduler has traditionally been bad. (If they
> did, perhaps it wouldn't have been so bad..)
> Plus all the I/O schedulers perform similarly with the usual benchmarks.
> With the exception of some tiobench phases, where AS does very well.
> Executive summary: the anticipatory scheduler is wiping the others off the
> map, and 2.4 is a disaster.
> I really have not sought to make the AS look good - I mainly concentrated on
> things which we have traditonally been bad at. If anyone wants to suggest
> other tests, please let me know.
> The known regressions from the anticipatory scheduler are:
> 1) 15% (ish) slowdown in David Mansfield's database run. This appeared to
> go away in later versions of the scheduler.
> 2) 5% dropoff in single-threaded qsbench swapstorms
> 3) 30% dropoff in write bandwidth when there is a streaming read (this is
> actually good).
> The test machine is a fast P4-HT with 256MB of memory. Testing was against a
> single fast IDE disk, using ext2.
> -
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