[lttng-dev] performance improvement, stop channel tracing, etc

[John Smith]

Hi,
I have a couple of questions, here they are:

1) tracing latency, on a simple loop tracing test I noticed the latency is
around 400ns on a 3.2GHz processor, are there ways to reduce this latency?
One thought about RCU, it is an efficient mechanism for multiple writers
but when there is a single source for the events, it may not be
necessary, my understanding is that the trace collection/read is done when
the sub-buffer is not been populated/written.

2) I noticed the log [delta] interval (2-nd value) is not actually the
difference between the two sequential traces (of the same event)
timestamps, did I miss anything and it represents something else or is a
bug?

3) Is there an api available to stop a channel tracing while session has
started ("lttng start") and of course before it has ended ("lttng stop")?
That would be useful if we want to stop tracing in case of critical events.

4) it would be useful if the tracepoint() (I know is a macro now) would
return some information about the success, overwrite or discard (depending
on the channel configuration) of the event, is it a way to get this
information currently?


thanks, John
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