Re: [PATCH v3 0/2] kstats: kernel metric collector

["Toke Høiland-Jørgensen" <toke@redhat.com>]

Luigi Rizzo <lrizzo@google.com> writes:

> This patchset introduces a small library to collect per-cpu samples and
> accumulate distributions to be exported through debugfs.
>
> This v3 series addresses some initial comments (mostly style fixes in the
> code) and revises commit logs.

Could you please add a proper changelog spanning all versions of the
patch as you iterate?

As for the idea itself; picking up this argument you made on v1:

> The tracepoint/kprobe/kretprobe solution is much more expensive --
> from my measurements, the hooks that invoke the various handlers take
> ~250ns with hot cache, 1500+ns with cold cache, and tracing an empty
> function this way reports 90ns with hot cache, 500ns with cold cache.

I think it would be good if you could include an equivalent BPF-based
implementation of your instrumentation example so people can (a) see the
difference for themselves and get a better idea of how the approaches
differ in a concrete case and (b) quantify the difference in performance
between the two implementations.

-Toke