[lttng-dev] add cpu_id context to the channel

Yonghong Yan yanyh15 at gmail.com
Mon Jan 21 16:21:47 EST 2019

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.


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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