[lttng-dev] add cpu_id context to the channel

[Yonghong Yan]

Thank you Genevieve, "cpu" field works.

Yonghong


On Mon, Jan 21, 2019 at 7:57 PM Genevieve Bastien <gbastien at versatic.net>
wrote:

> Hi Yonghong,
>
> With TraceCompass XML analyses, you can use as state value or attribute an
> eventField called 'cpu' to get the CPU id of an event. For example,
>
> <stateAttribute type="eventField" value="cpu" />
>
> With LTTng traces, it will automatically be the CPU, obtained as Mathieu
> described, no need for an extra field.
>
> Regards,
>
> Geneviève
>
>
> On 2019-01-21 4:21 p.m., Yonghong Yan wrote:
>
> Thank you. make sense. I am using Trace Compass XML based approach to
> display UST trace records. Using CPU id helps me easier to sort out the
> event records in trace compass. I will check out more on trace compass.
>
> Yonghong
>
>
> On Mon, Jan 21, 2019 at 2:06 PM Mathieu Desnoyers <
> mathieu.desnoyers at efficios.com> wrote:
>
>>
>> ----- On Jan 21, 2019, at 12:14 PM, Yonghong Yan <yanyh15 at gmail.com>
>> wrote:
>>
>> I saw there is cpu_id field in babeltrace list, how can I add it to the
>> context of UST tracepoint events. lttng add-context --list does not show
>> that field and I do not see a similar field for the cpu_id.
>>
>>
>> The cpu_id context only exists for the purpose of lttng-ust and
>> lttng-modules filtering.
>> (e.g. lttng enable-event {-u,-k} --filter '$ctx.cpu_id == 2').
>>
>> It is not possible to add it as context to the streams, because its
>> information would
>> be completely redundant with the fact that all the data is written into
>> per-cpu buffers,
>> and the cpu_id field is available within each packet context (which is
>> right after each
>> packet header).
>>
>> You just need to use babeltrace to convert to text, and while doing so,
>> it prints a
>> "cpu_id = N" context based on the packet_context cpu_id field for each
>> event.
>>
>> Thanks,
>>
>> Mathieu
>>
>> --
>> Mathieu Desnoyers
>> EfficiOS Inc.
>> http://www.efficios.com
>>
>
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