On 01/16/2015 09:24 PM, Mathieu Desnoyers wrote:
If you care about not overwriting your buffers under heavy load, I
recommend to issue "lttng stop; lttng snapshot record" in order to
stop tracing before gathering the snapshot. This would lessen the
chances to overwrite your important trace data due to your heavy
load.
Yeah, that perfectly makes sense. I tried this and it indeed helped to
not loose a single trace anymore! (without 'lttng stop' some 'snapshots'
still didn't contain what I was interested in). For the records, this is
how I currently use LTTng:
lttng create --snapshot victory
lttng enable-channel channel0 -k --subbuf-size 16M --num-subbuf 2
lttng add-context -k -t procname -c channel0
lttng enable-event -k --all -c channel0
for i in $(ps -mo tid -p `pgrep lttng-consumerd` | grep -v "TID" |
grep -v "-"); do sudo chrt -f -p 50 $i; done
lttng start
chrt -f 50 ./run_my_test-application_here # this app (programmed in
C/C++) performs a 'system("lttng stop; lttng snapshot record; lttng
start");' whenever a certain jitter is reached
lttng stop
lttng destroy
I guess the line:
for i in $(ps -mo tid -p `pgrep lttng-consumerd` | grep -v "TID" |
grep -v "-"); do sudo chrt -f -p 50 $i; done
wouldn't be necessary anymore (with 'lttng stop') but I didn't try that.
Cheers,
Raphael
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