----- On Nov 28, 2020, at 1:49 AM, 熊毓华 xiongyu...@zju.edu.cn wrote: > Hi,
> I put my test scripts in the attachment. > You can just run the script directly, create the trace session with the > "--live" > option on the 8core server, > then you will find the cpu usage of the lttng-consumerd process reached 10% or > more. > About the streaming mode of lttng,I did the test before, it worked well. > When I create the trace session with "lttng create my-session > --output=/tmp/my-kernel-trace", or with "lttng create my-session > --set-url=net://ip", > the number of CPU seems not affect the cpu usage with lttng-consumerd. > It seems that only live-mode will be affected. The overhead of consumer daemon in live mode will increase with the number of cpus on the system. This is expected. There is one knob you can try to configure to adapt the amount of overhead caused by the live timer in the consumer daemon: lttng create --live=NNN where NNN is the live timer period in microseconds. The default is 1000000us (1 second). Try changing this value to something larger and you will probably notice that it lessen the consumer daemon overhead. Shipping trace data with relatively low latency so it can be immediately read adds overhead, and it increases with the number of cpus in the system because there are then more per-cpu buffers to flush. Note that your instrumentation also targets unrelated kernel and user-space execution, so whatever is executed in the background also gets traced. And this generate trace data traffic on each cpu. Having even just a bit of trace data to send out in live mode can very much explain the overhead you observe with the lttng consumer daemon. If you care that much about overhead of the consumer daemon, don't use live mode, and use the alternatives we discussed earlier instead, such as the session rotation mode, if you need to consume the trace data while it is produced. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com _______________________________________________ lttng-dev mailing list lttng-dev@lists.lttng.org https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
