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
>