Since the GC can sometimes cause delays that can make problems for latency-sensitive programs, it may be useful to notice when it has run.

To that end, I've adapted Brendan Gregg's killsnoop ( https://github.com/brendangregg/perf-tools/blob/master/killsnoop ) to gcsnoop, a tool to supervise tgkill syscalls (used by the GC for SIGUSR1/SIGUSR2) and log time, PID and GC delay.

https://gist.github.com/FeepingCreature/a2efe19f15eb582af274b23002c25706

Since it uses the kernel event tracing API, it needs to run as root.

Time is seconds since boot.

Sample output:

$ sudo ./gcsnoop  -t
Tracing GC runs. Ctrl-C to end.
TIMEs            COMM             PID        TGID       LENGTH
355487.807757    gctest-360995    360996     360995     1.364406
355489.930831    gctest-360995    360996     360995     1.291132
355492.119666    gctest-360995    360996     360995     1.403598
355494.446310    gctest-360995    360996     360995     1.543637
^C
Ending tracing...

On Friday, 23 July 2021 at 08:16:03 UTC, FeepingCreature wrote:

Ohh nice. That will be useful! Thank you for the post :)