Re: [PATCH 00/32] tracing: Inter-event (e.g. latency) support

From: Joel Fernandes (Google)
Date: Sat Jul 01 2017 - 03:02:42 EST

Hi Tom,
Nice series and nice ELC talk as well. Thanks.

On Mon, Jun 26, 2017 at 3:49 PM, Tom Zanussi
<tom.zanussi@xxxxxxxxxxxxxxx> wrote:
> This patchset adds support for 'inter-event' quantities to the trace
> event subsystem. The most important example of inter-event quantities
> are latencies, or the time differences between two events.

I tried your patches out and they are working fine for me. I will test
them out more.

I think for the wakeup latency in your examples, its better / more
accurate to use sched_waking instead of sched_wakeup tracepoint? [1]

Also, one other comment I had is, it would be nice to suppress the
output of individual trace events that are part of the synthetic event
into the trace buffer. Otherwise I feel the value of it is slightly
diminished - because one can simply post-process the individual
non-synthetic trace events themselves to get wake up latencies which
the synthetic events is trying to calculate in the first place.
Inorder to conserve space, if a user doesn't care about individual
events, and just the synthetic events then the individual ones
shouldn't be written to the trace buffer IMO.


[1] commit fbd705a0c6184580d0e2fbcbd47a37b6e5822511 (sched: Introduce
the 'trace_sched_waking' tracepoint)