Re: Kernel 2.4.x and 2.4.1-preX - Higher latency then 2.2.xkernels?

[Andrew Morton <andrewm@uow.edu.au>]

Shawn,

I've pretty much completed the low-latency patch against reiserfs.
It seems to be a little more latency-prone than ext2, but under normal
workloads it's not significant.  The worst-case is 100 milliseconds,
but that's when you're doing insane things to it.

You may care to apply http://www.uow.edu.au/~andrewm/linux/2.4.1-pre10-low-latency.patch
against 2.4.1-pre10 and see if it "feels" different.  I'd be surprised
if it does, but the result would be interresting.

Note that the low-latency capability must be enabled under the
"Processor type and features" menu, and if you also enable the
low-latency sysctl option, you'll need to

	echo 1 > /proc/sys/kernel/lowlatency

to make it happen.  Creature feep :)


Shawn Starr wrote:
> 
> Sure, but Im not sure what to test ;)
> If you've got any special patches for 2.4 lemme know and I'll apply them I've
> got all night heh
> 
> Shawn.
> 
> Chris Mason wrote:
> 
> > On Saturday, January 20, 2001 02:59:24 PM -0500 Gregory Maxwell
> > <greg@linuxpower.cx> wrote:
> >
> > > On Sat, Jan 20, 2001 at 02:50:16PM -0500, Shawn Starr wrote:
> > >> It just seems that since using 2.4 ive noticed my poor Pentium 200Mhz
> > >> slow down whether being in X or otherwise. It just seems that the system
> > >> is sluggish.
> > >>
> > >> I am using the new ReiserFS filesystem and I do know its still in heavy
> > >> development perhaps my latency is due to this (?)
> > >
> > > Reiserfs uses much more complex data structures then ext2 (trees..). I
> > > don't think that latency has ever been a design criteria and all of the
> > > benchmarks they use are pretty much pure throughput tests.
> > >
> > > So it wouldn't be really surprising if reiserfs had very bad latency. You
> > > should apply the timepegs patch and profile your kernel latency to see
> > > where it's coming from.
> >
> > I'm actually very interested in fixing any latency problems.  If you do
> > these tests, please send the results along.
> >
> > -chris
> > -
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