Hi, On Fri, Nov 27, 2020 at 02:39:28PM +0800, 熊毓华 via lttng-dev wrote: > Hi，dear. > > I have been using lttng to monitor my server these days，but I found something > interesting. > > The cpu usage of lttng varies with the number of cpu cores of the server.
Which is a bit expected since more CPU means more "data" source from the point of view of lttng hence more "work" overall. > > On the server, I create a tracing session in live mode, using "lttng create > my-session --live". > > Then,I Start the babeltrace2 and configure it to connect to the relay > daemon,using "--input-format=lttng-live" mode. > > I used 5 cloud servers，1core4G 2core8G 4core16G 8core16G 8core16G. > > And,the same test script was executed above to provide the same workload. We would need the test script to have some context here of the workload. > > As we all know,lttng has 5 processes, > > 1.lttng-runas --daemonize > > 2.lttng-runas -k --consumerd-cmd-sock /var/run/lttng/kconsumerd/command > --consumerd-err-sock /var/run/lttng/kconsumerd/error --group tracing Based on this you are performing kernel tracing. > > 3.lttng-sessiond --daemonize > > 4.lttng-relayd -L tcp://localhost:5344 > > 5.lttng-consumerd -k --consumerd-cmd-sock /var/run/lttng/kconsumerd/command > --consumerd-err-sock /var/run/lttng/kconsumerd/error --group tracing > > > The CPU usage of the first four processes is below 2% on the 5 servers,but > the lttng-consumerd process is different. > > On 1-core、2-core、4-core servers，the CPU usage of the lttng-consumerd process > is below 2%. How is the cpu usage measured here? > > But on two 8-core machines, the cpu usage of the lttng-consumerd process > reached 10% or more. Consumerd is responsible of "fetching" data from the ring buffers and "saving" it either locally (trace on disk) or remotely (streaming/live session). CPU usage should be a bit correlated with the event production rate. Did you have a look at the number of events generated for a similar interval? > And,the cpu usage of the babeltrace process is not much different,just the > cpu usage of the lttng-consumerd process varies with the number of cpu cores > of the server. > > Why it is like this？How should this phenomenon be analyzed? > > Looking forward to your reply. > > thanks, > yuhua > > _______________________________________________ > lttng-dev mailing list > lttng-dev@lists.lttng.org > https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev -- Jonathan Rajotte-Julien EfficiOS _______________________________________________ lttng-dev mailing list lttng-dev@lists.lttng.org https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
