Re: HPL benchmarking linux kernel for shared memory performance.

[Marcin Slusarz <marcin.slusarz@gmail.com>]

On Sun, Mar 16, 2008 at 01:38:51AM -0400, Allan Menezes wrote:
> Hi,
>    I eliminated in which kernel verion this begins to happen. I am 
> benchmarking a single node with hpl and openmpi beta 1.3 and gotoblas v1.24
> for personal noncommercial reasons.
> I tried a single node with the command $ mpirun -np 1 ./xhpl
> and with kernel ver 2.6.23.14 i get over 38Gflops
> but with kernel ver 2.6.23.15 compiling with the same .config i get 7.xx 
> Gflops which is 1/5th that of the other kernel.
> Keep in mind that only the kernels have changed from kernel.org not any 
> hardware or anything else as all else is same! but the  performace drops to 
> 1/5th
> There is no network involved in this single node quad core intel test but 
> just shared memory.
> So the shared memory or smp performance of the newer kernels is far far 
> worse than upto 2.6.23.14!
> Even with 2.6.25.rc5 the performance is degraded!
> Can you please help me find why this is occurring? Please advise!
> mY set up Quad core Q6600 intel overclocked stably to 2.88 GHZ , 6 gig ddr2 
> 800 mhz dual channel ram,
> Allan Menezes

If you want to speed up bug resolution, you can bisect it to only one patch with git
(google for git bisect) on this tree:
git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-2.6.23.y.git

ps: please post your .config and dmesg output

Marcin