Hello group!

When we migrate from 2.4.20 kernel to the various 2.6.x kernel versions we
have noticed severe degradation in the lmbench context switch benchmark on
the various dual Xeon SMP blades. On the single CPU blades everything works
OK. Also other benchmarks in the lmbench shows comparable results between
2.4.20 and 2.6.x kernels.

We found that on 2.6.x disabling the SMP support in kernel actually
increases the lmbench context switch result. On 2.4.20 disabling the SMP
support decreased performances (logically). Also using CPU affinity to lock
processes to cores helps. But still we are far away from results we achieved
with 2.4.20 kernel.

As our application uses a lot of message passing and processes context
switches we are not able to utilize SMP CPU blades or multicore CPU under
2.6 kernels as we expect.

Did anyone encounter similar problem? Any suggestion what to do?

Regards,

Sani

Sani Rus wrote:

> Hello group!
>
> When we migrate from 2.4.20 kernel to the various 2.6.x kernel versions we
> have noticed severe degradation in the lmbench context switch benchmark on
> the various dual Xeon SMP blades. On the single CPU blades everything
> works OK. Also other benchmarks in the lmbench shows comparable results
> between 2.4.20 and 2.6.x kernels.
>
> We found that on 2.6.x disabling the SMP support in kernel actually
> increases the lmbench context switch result. On 2.4.20 disabling the SMP
> support decreased performances (logically). Also using CPU affinity to
> lock processes to cores helps. But still we are far away from results we
> achieved with 2.4.20 kernel.
>
> As our application uses a lot of message passing and processes context
> switches we are not able to utilize SMP CPU blades or multicore CPU under
> 2.6 kernels as we expect.
>
> Did anyone encounter similar problem? Any suggestion what to do?
>
> Regards,
>
> Sani

Unless your application requires features of a 2.6 kernel, it would appear
for your application (if it requires that particular feature) to remain on
a 2.4 kernel.
It might be be worth while getting in touch with your distro's support or
perhaps the kernel mailing list, it could be that there is setting to
optimise this in a 2.6 kernel.

Bruce S.
--
Replace the by by blueyonder