Re: [Issue] access cpu_cycles PMU conter in r8a7791

[Chai Wen <chaiw.fnst@cn.fujitsu.com>]

On 10/17/2014 01:15 PM, Magnus Damm wrote:

> Hi Chai Wen,
> 
> On Wed, Oct 15, 2014 at 2:13 PM, Chai Wen <chaiw.fnst@cn.fujitsu.com> wrote:
>> Hi developers,
>>
>> Sorry for some disturbing.
>>
>> I am planing to use pmu counter cpu_cycles to measure the elapsed time of some small pieces of code.
>> But I found that I can not make the PMU work properly.
>>
>> My cpu is called r8a7791, a 2-core cpu. And the kernel version is 3.10.31.
>> The following is my simple code to test it and its result.
>>
>> I found that no matter what's the scale of this loop:
>>         for (i = 0; i < loops; i++) {
>>                 __asm__ __volatile__("mov r0, r0\n\t");
>>         }
>>         the cycles counts got via:
>>         __asm__ __volatile__("MRC p15, 0, %0, c9, c13, 0\n\t" : "=r"(count));
>>         are not significantly different from each other. I am confused about these values.
>>
>> Any comment or help is appreciated, thanks a lot.
> 
> I'm not aware of any known issue like this, however I do notice that
> you are using a rather old kernel version. The kernel version may be
> unrelated to the root cause of your issue, however from a community
> stand point I recommend that you try to reproduce this issue on the
> latest upstream with the most recent boot loader for your board. If
> upstream is not working then we need to fix that first.


Hi Magnus Damm

thanks for your reply.

I will try this on the latest upstream kernel version.


thanks
chai wen

> 
> Cheers,
> 
> / magnus
> .
> 



-- 
Regards

Chai Wen