Re: performance "regression" in cfq compared to anticipatory, deadline and noop

[Kasper Sandberg <lkml@metanurb.dk>]

On Tue, 2008-05-13 at 14:20 +0200, Jens Axboe wrote:
> On Sun, May 11 2008, Kasper Sandberg wrote:
> > On Sun, 2008-05-11 at 14:14 +0100, Daniel J Blueman wrote:
> > > I've been experiencing this for a while also; an almost 50% regression
> > > is seen for single-process reads (ie sync) if slice_idle is 1ms or
> > > more (eg default of 8) [1], which seems phenomenal.
<snip>
> > 
> > Thisd would appear to be quite a considerable performance difference.
> 
> Indeed, that is of course a bug. The initial mail here mentions this as
> a regression - which kernel was the last that worked ok?

I am afraid i cannot exactly tell you..

But i do have some additional information for you.

I have a server running with identical disk to mine, however, with an
older intel ahci controller..

This one gets 80mb/s with cfq, and 100mb/s with
anticipatory/deadline/noop with hdparm..

This server is running debian stable with a .18 kernel. I am sad to say
however, that i will be unable to do any testing on this box, since it
is a production server, and i can not shut it down.

haltek:~/blktrace# ./blktrace  /dev/sda
BLKTRACESETUP: Inappropriate ioctl for device
Failed to start trace on /dev/sda

However, on the box where you saw the previous numbers, i sure will be
able to provide you with the data you need.

i expect to get around to doing this this afternoon, or tonight at
~02:00
(im GMT+1).


> 
> If someone would send me a blktrace of such a slow run, that would be
> nice. Basically just do a blktrace /dev/sda (or whatever device) while
> doing the hdparm, preferably storing output files on a difference
> device. Then send the raw sda.blktrace.* files to me. Thanks!
>