ARM cortex A9 performance issue

[dave.martin@linaro.org (Dave Martin)]

On Thu, Jul 07, 2011 at 02:48:05PM +0530, rd bairva wrote:
> Hi,
> 
> We are trying to benchmark ARM cortex A9 dual core behavior with
> respect to single core
> performance and also measuring it with respect to x86 dual core/single core.
> Please find attached with the mail is c app which we are using for benchmarking.
> 
> Simple overview of C application:
> - It creates a shared memory area using shm_open().
>   in this shm area, it declares 2 Process shared pthread mutex, lets say L1, L2.
> - then it forks to create a server_task and client task.
> - server_task takes L1 lock, touches a shm area, unlock L2, in a loop.
> - client_task takes L2 lock, touches a shm area, unlock L1, in a loop.
> - This loop runs for N number of times that we measure.

The behaviour of pthread_mutex_unlock is unspecified if an attempt is made
to ulock a mutex from a thread which doesn't currently own that mutex.
You probably need to re-code your test to avoid this incorrect use of
the ABI before an interpretation can be placed on the results.

See pthread_mutexattr_init(3) for details.



Some people have been reported issues related to  process shared mutexes
on ARM recently:

https://bugs.launchpad.net/ubuntu/+source/apr/+bug/604753

I'm not sure of the current status of that though, and I don't know
whether it would affect your test or not.

Cheers
---Dave

> 
> Here are the results for N/sec for different CPUs.
> 
> Platform              Up cores              req/sec                cpuload
> Cortexa9                    2                              ~44000
>             100%
> Cortexa9                    1                              ~18000
>             100%
> X86                            2                              ~64000
>                35%
> X86                            1                              ~458886
>              100%     (1 cpu down by sysfs)
> 
> we are not able to understand the results.
> - why for coretx A9 both dual/single core we are getting 100% cpu usage.
> - why in case of x86, N/sec is very high for single core than dual core.
> - why single core N/s is 1/3 in case of CortexA9.
> 
> Thanks,
> Ramdayal


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