linux-kernel - Re: [PATCH v2 3/3] perf lock: Print the number of lost entries for BPF

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Date:   Mon, 26 Sep 2022 14:42:21 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Jiri Slaby <jirislaby@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ian Rogers <irogers@...gle.com>,
        linux-perf-users <linux-perf-users@...r.kernel.org>,
        Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Song Liu <songliubraving@...com>,
        Blake Jones <blakejones@...gle.com>
Subject: Re: [PATCH v2 3/3] perf lock: Print the number of lost entries for BPF

Hello,

On Mon, Sep 26, 2022 at 1:05 AM Jiri Slaby <jirislaby@...nel.org> wrote:
>
> Hi,
>
> On 02. 08. 22, 21:10, Namhyung Kim wrote:
> > Like the normal perf lock contention output, it'd print the number of
> > lost entries for BPF if exists or -v option is passed.  Currently it
> > uses BROKEN_CONTENDED stat for the lost count (due to full stack maps).
> ...
> > --- a/tools/perf/util/bpf_skel/lock_contention.bpf.c
> > +++ b/tools/perf/util/bpf_skel/lock_contention.bpf.c
> ...
> > @@ -73,6 +73,9 @@ int enabled;
> >   int has_cpu;
> >   int has_task;
> >
> > +/* error stat */
> > +unsigned long lost;
>
> I don't know how all this is generated into lock_contention.skel.h. But
> I believe this patch breaks perf build on 32bit:
> > [  375s] In file included from util/bpf_lock_contention.c:13:
> > [  375s] util/bpf_skel/lock_contention.skel.h: In function 'lock_contention_bpf__assert':
> > [  375s] util/bpf_skel/lock_contention.skel.h:537:9: error: static assertion failed: "unexpected size of \'lost\'"
> > [  375s]   537 |         _Static_assert(sizeof(s->bss->lost) == 8, "unexpected size of 'lost'");
> > [  375s]       |         ^~~~~~~~~~~~~~
>
> Should the above (and below too) be __u64?

Oops, it seems BPF ABI uses 8-byte long even on 32-bit systems.
Sorry for the inconvenience.  Will change.

Thanks,
Namhyung


>
> > --- a/tools/perf/util/lock-contention.h
> > +++ b/tools/perf/util/lock-contention.h
> > @@ -113,6 +113,7 @@ struct lock_contention {
> >       struct machine *machine;
> >       struct hlist_head *result;
> >       unsigned long map_nr_entries;
> > +     unsigned long lost;
>
> thanks,
> --
> js
> suse labs
>