Hi,
I am observing a performance issue with regards to enabling events while a
session is active and was wondering if this is expected.
LTTng versions:
* lttng-tools: 2.13.9
* lttng-ust: 2.13.6
Steps to reproduce:
1. Ensure many userspace tracepoints are available in `lttng list -u` e.g.
100
2. Create a new session
3. Start session
4. Enable new events on session
The time it takes to enable each new event has increasing cost e.g.
1. Event 1: 1ms
2. Event 100: 15ms
3. Event 1000: 150ms
4. --> in total about 1.5 minutes to enable 1000 events
If either:
1. No userspace tracepoints are available
2. Or session is not started until after the events are enabled
Then the time it takes to enable new events is constant (e.g. 1ms).
Below is a bash script demonstrating this behavior:
# Pre-requisite: have many userspace tracepoints available
lttng create foo
lttng enable-channel -u -s foo bar
lttng start foo
total_t1=$(date +%s%3N);
for i in {1..100}
do
t1=$(date +%s%3N);
lttng enable-event -u lttng_iter_$i -s foo -c bar > /dev/null
t2=$(date +%s%3N);
echo "Event #$i took $((t2-t1)) ms"
done
total_t2=$(date +%s%3N);
echo "----------------------------------------------------"
echo "Enabling events on active session took $((total_t2-total_t1)) ms"
echo "----------------------------------------------------"
lttng destroy foo
lttng create foo
lttng enable-channel -u -s foo bar
total_t1=$(date +%s%3N);
for i in {1..100}
do
t1=$(date +%s%3N);
lttng enable-event -u lttng_iter_$i -s foo -c bar > /dev/null
t2=$(date +%s%3N);
echo "Event #$i took $((t2-t1)) ms"
done
total_t2=$(date +%s%3N);
echo "----------------------------------------------------"
echo "Enabling events on inactive session took $((total_t2-total_t1)) ms"
echo "----------------------------------------------------"
lttng destroy foo
Is this reproducible for you? Any insight is appreciated.
Many thanks,
Zach
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