bad lmbench results on 2.6.x kernel with SMP

Sani Rus wrote:
[color=blue]
> 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[/color]

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.
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