Re: io performance...

[Max Waterman <davidmaxwaterman+kernel@fastmail.co.uk>]

Unfortunately, they don't want me to spend time doing this sort of 
thing, so I'm out of luck.

They're going to stick with 2.6.8-smp, which seems to give the best 
performance (which rules out your second case below, I suppose).

:|

Max.

Adrian Bunk wrote:
> On Mon, Jan 16, 2006 at 03:35:31PM +0800, Max Waterman wrote:
> > Hi,
> >
> > I've been referred to this list from the linux-raid list.
> >
> > I've been playing with a RAID system, trying to obtain best bandwidth
> > from it.
> >
> > I've noticed that I consistently get better (read) numbers from kernel 2.6.8
> > than from later kernels.
> >
> > For example, I get 135MB/s on 2.6.8, but I typically get ~90MB/s on later
> > kernels.
> >
> > I'm using this :
> >
> > <http://www.sharcnet.ca/~hahn/iorate.c>
> >
> > to measure the iorate. I'm using the debian distribution. The h/w is a 
> > MegaRAID
> > 320-2. The array I'm measuring is a RAID0 of 4 Fujitsu Max3073NC 15Krpm 
> > drives.
> >
> > The later kernels I've been using are :
> >
> > 2.6.12-1-686-smp
> > 2.6.14-2-686-smp
> > 2.6.15-1-686-smp
> >
> > The kernel which gives us the best results is :
> >
> > 2.6.8-2-386
> >
> > (note that it's not an smp kernel)
> >
> > I'm testing on an otherwise idle system.
> >
> > Any ideas to why this might be? Any other advice/help?
>
> You should try to narrow the problem a bit down.
>
> Possible causes are:
> - kernel regression between 2.6.8 and 2.6.12
> - SMP <-> !SMP support
> - patches and/or configuration changes in the Debian kernels
>
> You should try self-compiled unmodified 2.6.8 and 2.6.12 ftp.kernel.org 
> kernels with the same .config (modulo differences by "make oldconfig").
>
> After this test, you know whether you are in the first case.
> If yes, you could do a bisect search for finding the point where the 
> regression started.
>
> > Thanks!
> >
> > Max.
>
> cu
> Adrian

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