On Fri, 06 Jun 2025 15:13:05 +0200 Bert Karwatzki <spasswolf@xxxxxx> wrote: > I tried this and first thought my kernel did not have the right configuration as > > # trace-cmd record -e preempt_disable -e preempt_enable > > seemed to do nothing in particular, but it turns out it takes a long time to start > (~1min) when the kernel is compiled with CONFIG_LOCKDEP=y. (on the standard debian Yeah, that's a recent regression in the code which I'm currently testing a fix for: https://lore.kernel.org/linux-trace-kernel/20250605161701.35f7989a@xxxxxxxxxxxxxxxxxx > kernel starting to record takes less time, but it does not have CONFIG_PREEMPT_TRACER.) > > So after the trace-cmd was running I ran the bpf example and got a trace.dat: > > # ls -lh trace.dat > -rw-r--r-- 1 root root 152M 6. Jun 14:41 trace.dat > > turning this into a report with > > # trace-cmd report > preemp_trace.rep > > gives a rather unwieldly large file Of course, it's recording every time preemption is enabled and disabled ;-) I usually run it with a test: # trace-cmd record -e preempt_disable -e preempt_enable ./myprog Where it will stop when ./myprog is done. > > # ls -lh preempt_trace.rep > -rw-rw-r-- 1 root root 7,4G 6. Jun 14:46 preempt_trace.rep > > This file has about 61 million lines > > # wc -l preempt_trace.rep > 61627360 preempt_trace.rep > > but only 742104 corresponding to the bpf example program "test_progs" > > # grep test_progs preempt_trace.rep | wc -l > 742104 # trace-cmd record -e preempt_disable -e preempt_enable -F ./test_progs where "-F" means "follow" and will only record when "./test_progs" is running. Add "-c" to also trace its children. > > Is it possible to filter the preempt_{en,dis}able events by task name (i.e. > get_current()->comm)? > > I tried this (from https://code.tools/man/1/trace-cmd-report/) but it > fails with an error message: > # trace-cmd record -e preempt_enable -F '.*:COMM == "test_progs"' -e preempt_disable -F '.*:COMM == "test_progs"' -F means to execute. The -F in trace-cmd report is filter (that's because -f was already taken :-p) -- Steve > > ******************** > Unable to exec .*:COMM == "test_progs" > ******************** > trace-cmd: No such file or directory > Failed to exec .*:COMM == "test_progs" > libtracecmd: No such file or directory > can not stat 'trace.dat.cpu0' > > > Bert Karwatzki
