Changing frequency rate to perf mem

Changing frequency rate to perf mem

[Harald Servat]

Hello list,

   I'm interested on changing the frequency rate to the perf mem tool. I 
understand that this tool captures the data every N loads or stores, 
however I don't see how to tune N.

   I've looked into builtin-record.c approx line 980 and I found that 
changing rec->opts.freq allows me capturing more or less data. 
Initially, its value is 4000 and generates 4.5Mbytes for an application. 
If I modify this value to 200, it generates 0.2Mbytes, therefore 
200/4000 is closely 0.2/4.5 which seems the value I want to tune.

   I'd like to know what is this rec->opts.freq with respect to perf 
mem. I expected to setup the number of loads, therefore the higher N the 
lesser number of samples generated, but it seems the other way around. 
Where I can get any hint on what does this mean.

   BTW, I tried to change this value by adding "-F" and "200" into the 
argv that is passed to cmd_report by adding

         rec_argv[i++] = strdup("-F");
         rec_argv[i++] = strdup("200");

   into line 42 of perf-mem.c - just after the strdup("record"). 
Unfortunately, this seems to break something and perf segfaults often. 
Which is the most appropriate way to tune the user frequency of perf mem?

Thank you very much in advance!

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Re: Changing frequency rate to perf mem

[Andi Kleen]

Harald Servat <harald.servat@bsc.es> writes:
>
>   BTW, I tried to change this value by adding "-F" and "200" into the
> argv that is passed to cmd_report by adding
>
>         rec_argv[i++] = strdup("-F");
>         rec_argv[i++] = strdup("200");
>
>   into line 42 of perf-mem.c - just after the
> strdup("record").

You would need to increase the array size too.

> Unfortunately, this seems to break something and
> perf segfaults often. Which is the most appropriate way to tune the
> user frequency of perf mem?

Best would be probably to fix it to pass through unknown
options, then -F/-c could be just used. I'm not sure
if this is possible easily with the git option parser.

Alternatively you can just specify the command line perf mem record
would specify directly to perf record, plus -c/-F

-andi

-- 
ak@linux.intel.com -- Speaking for myself only

Re: Changing frequency rate to perf mem

[Harald Servat]

On 24/10/13 07:12, Andi Kleen wrote:
> Harald Servat <harald.servat@bsc.es> writes:
>>
>>    BTW, I tried to change this value by adding "-F" and "200" into the
>> argv that is passed to cmd_report by adding
>>
>>          rec_argv[i++] = strdup("-F");
>>          rec_argv[i++] = strdup("200");
>>
>>    into line 42 of perf-mem.c - just after the
>> strdup("record").
>
> You would need to increase the array size too.

Ouch! You're right! I forgot that!

>
>> Unfortunately, this seems to break something and
>> perf segfaults often. Which is the most appropriate way to tune the
>> user frequency of perf mem?
>
> Best would be probably to fix it to pass through unknown
> options, then -F/-c could be just used. I'm not sure
> if this is possible easily with the git option parser.

Sorry, I'm not sure what is the "git option parser" here.
I think that this could be implemented extending the mem_options[] in 
file builtin-mem.c lines 205-221.

> Alternatively you can just specify the command line perf mem record
> would specify directly to perf record, plus -c/-F
>
> -andi
>

Thank you very much Andi.
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Re: Changing frequency rate to perf mem

[Namhyung Kim]

Hi Harald,

On Thu, 24 Oct 2013 09:48:09 +0200, Harald Servat wrote:
> On 24/10/13 07:12, Andi Kleen wrote:
>> Harald Servat <harald.servat@bsc.es> writes:
>>> Unfortunately, this seems to break something and
>>> perf segfaults often. Which is the most appropriate way to tune the
>>> user frequency of perf mem?
>>
>> Best would be probably to fix it to pass through unknown
>> options, then -F/-c could be just used. I'm not sure
>> if this is possible easily with the git option parser.
>
> Sorry, I'm not sure what is the "git option parser" here.

Just implementation details.  The source code of the option parser came
from the git project.


> I think that this could be implemented extending the mem_options[] in
> file builtin-mem.c lines 205-221.

Or else, use 'perf record' directly as Andi suggested.

>
>> Alternatively you can just specify the command line perf mem record
>> would specify directly to perf record, plus -c/-F

  $ perf record -Wd -e cpu/mem-loads/pp -F 200 -- ls

  $ perf mem report


Thanks,
Namhyung

Re: Changing frequency rate to perf mem

[Harald Servat]

>> I think that this could be implemented extending the mem_options[] in
>> file builtin-mem.c lines 205-221.
>
> Or else, use 'perf record' directly as Andi suggested.
>
>>
>>> Alternatively you can just specify the command line perf mem record
>>> would specify directly to perf record, plus -c/-F
>
>    $ perf record -Wd -e cpu/mem-loads/pp -F 200 -- ls
>
>    $ perf mem report
>

Wow, thank you for such details! I'll take a look at this!

Best regards.


> Thanks,
> Namhyung
>


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