[lttng-dev] scale numbers for LTTNG

[vjanandr85@gmail.com (Vijay Anand)]

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Hi Mathieu, Jonathan,

I have written python scripts to simulate our requirements.
https://github.com/vjanandr/sampleP/tree/master/lttng

Please refer to the README file for further details about the scripts.

Mathieu, I understand your recommendation to use per UID buffers instead of
per PID buffers.
But I dont seem to understand your suggestion to use filters...

>>>>
Why ? You can always collect trace data into buffers shared across
processes (per-uid buffers)
and filter after the fact.
<<<<<

Did you mean to say write all traces to a file but filter them while
reading based on maybe process ID ?

Regards,
Vijay

On Fri, May 27, 2016 at 1:16 AM, Mathieu Desnoyers <
mathieu.desnoyers at efficios.com> wrote:

>
>
> ----- On May 26, 2016, at 8:23 AM, Vijay Anand <vjanandr85 at gmail.com>
> wrote:
>
> Could anyone please let us know how do we go about this ?
>
> Regards,
> Vijay
>
> On Tue, May 24, 2016 at 11:31 AM, Vijay Anand <vjanandr85 at gmail.com>
> wrote:
>
>> Hello Folks,
>>
>> We have been evaluating LTTNG for use in our production systems for user
>> space tracing. We have evaluated most of the features supported by LTTNG
>> and very much see a value add LTTNG brings into our debugging
>> infrastructure.
>>
>>    - Our current requirement is to trace Userspace programs running on
>>    linux.
>>    - Each of the linux processes define their own tracepoint providers.
>>
>>
> Sounds like a good design.
>
>
>>    -
>>    - We would like to trace event histories of each process
>>    independently.
>>
>>
> Why ? You can always collect trace data into buffers shared across
> processes (per-uid buffers)
> and filter after the fact.
>
>
>>    -
>>    - We could potentially have 1000s of such processes running
>>    simultaneously.
>>
>>
> Especially with that many processes, having per-process buffers will
> degrade your cache
> locality.
>
>
>>    -
>>    - We concluded on using a session/channel to trace one tracepoint
>>    provider corresponding to a unique process.
>>       - But I understand we could also create one system wide session
>>       and use channels to trace each of the providers. Either of the approaches
>>       seems to work for us.
>>
>> Both approach will kill you cache locality with that many process. I
> don't recommend either
> of the two approaches you refer to above. You might want to consider
> sharing your buffers
> across processes.
>
>
>>    - But upon evaluating I see that we could create only 25 active
>>    process-sessions and not traces from all the processes are logged.
>>
>> We will need much more details on your tracing configuration setup (exact
> list of commands you
> issue to create your tracing sessions).
>
> Also please detail what you mean by "not traces from all the processes
> are logged".
> What commands do you issue, what is the exact setup, and what is the output
> you observe (exact listing) which leads you to reach this conclusion.
>
> Thanks,
>
> Mathieu
>
>
>>    - Please note I have tried increasing the buffer size and the number
>>       of buffers. This doesn't help.
>>       - Each of the process trace 52 events at and interval of 1 second
>>       each.
>>    - I have evaluated this with lttng in session,live and snapshot modes
>>    and I have not been getting favourable.
>>
>> Could you folks share the scale numbers that LTTNG supports, especially
>> when it comes to tracing user space programs ?
>>
>> Regards,
>> Vijay
>> ​​
>>
>
>
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com
>
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