On Fri, 17 Jan 2025 13:04:07 +0100
Tomas Glozar [off-list ref] wrote:

I was thinking of turning timerlat_hist_handler/timerlat_top_handler
into a BPF program and having it executed right after the sample is
created, e.g. by using the BPF perf interface to hook it to a
tracepoint event. The histogram/counter would be stored in BPF maps,
which would be merely copied over in the main loop. This is
essentially how cyclictest does it, except in userspace. I expect this
solution to have good performance, but the obvious downside is that it
requires BPF. This is not a problem for us, but might be for other
rtla users and we'd likely have to keep both implementations of sample
processing in the code.

Also, before even starting with that, it would be likely necessary to
remove the duplicate code throughout timerlat/osnoise and test it
properly, so we don't have to do the same code changes twice or four
times.

We could also add kernel helpers to the code if it would help.

Hmm, the timerlat event could probably get access to a trigger to allow it
to do the work in the kernel like what the 'hist' triggers do. We can
extend on that.

The reason I haven't written a BPF program yet, is because when I feel
there's a useful operation that can be done, I just extend ftrace to do it
;-)

-- Steve