Re: Sample memory references with at least a given latency?

[Harald Servat <harald.servat@bsc.es>]

Hello,

On 05/02/15 12:33, Manuel Selva wrote:
> Hi Harald,
>
> You are right, the perf mem tool dosn't support stting the latency
> threshold. It should be a very easy first contribution to kernel for
> myself ;-)

   that would be great. If I had some spare time & a machine to mess a 
bit, I'd gladly help you. BTW, do you know if there's any alternative 
for developing the kernel?

> Regarding the timestamp, I nver need such information, but as you said
> you can't tll to the hardware (on Intel I mean) to record it along with
> processor state information. I don't know how th kernel part of perf
> configure PEBS, but why would the kernel pay the overhead of an
> interrupt by using 1 slot buffers ? Only for recording timestamp ?

   Personally, I play with time-stamped trace-files and find capturing 
the time-stamp extremely important! Andi Kleen (also from this list) 
confirmed this (1 slot buffer) but he didn't mention the exact reason. 
Still, and let me insist, this is perfect for my purposes so I'm ok with 
it. See previous mails from this ML:

http://article.gmane.org/gmane.linux.kernel.perf.user/1398/match=information+regarding+perf+tool

http://article.gmane.org/gmane.linux.kernel.perf.user/1375/match=information+regarding+perf+tool

Regards.


> ----
> Manu
>
> On 02/04/2015 03:20 PM, Harald Servat wrote:
>>
>> Hello Manuel,
>>
>>    I'm running Linux 3.11 but I don't see a way to setup the latency
>> threshold there. My option flags include:
>>
>>         -t, --type=
>>         -D, --dump-raw-samples=
>>         -x, --field-separator
>>         -C, --cpu-list
>>
>>    so I guess that this option is not implemented in perf (at least on
>> 3.11). So I need to capture all the samples and then discard those that
>> surpass that threshold.
>>
>>    Going back into your example, is it possible to capture / show the
>> timestamp for the captured samples? I've seen the Intel documentation,
>> and there aren't timestamps in PEBS entries so that may require
>> additional work. IIRC, someone of the list told me that perf allocates a
>> 1-entry PEBS buffer so every time PEBS fills it, perf somehow gets an
>> interrupt indicating that it has to flush it. This way, perf can
>> attribute a timestamp to that sample also.
>>
>> Thank you very much!
>>
>>
>> On 04/02/15 15:00, Manuel Selva wrote:
>>> Hi Harald,
>>>
>>> Yes you can with the "perf mem" tool. It has been introduced in kernel
>>> 3.10 (correct me if I am wrong, not very sure about that). It's built on
>>> top of perf mem record and perf mem report but hide for you the
>>> complxity of choosing the memory events . See "man perf mem" for th
>>> details.
>>>
>>> ----------
>>> Manuel
>>>
>>>
>>>
>>> 2015-02-04 13:48 GMT+01:00 Harald Servat <harald.servat@bsc.es
>>> <mailto:harald.servat@bsc.es>>:
>>>
>>>     Hello list,
>>>
>>>        is there any way to configure perf to sample memory references
>>>     through PEBS and enable the Load Latency Performance Monitoring
>>>     Facility (section 18.7.1.2 from the Intel 64 and IA-32 Architectures
>>>     Software Developer's Manual).
>>>
>>>     Thank you very much in advance.
>>>
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>>
>>
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