On Fri, Feb 3, 2023 at 10:31 AM Yonghong Song <yhs@xxxxxxxx> wrote:
>
>
>
> On 2/1/23 10:25 PM, Jon Doron wrote:
> > From: Jon Doron <jond@xxxxxx>
> >
> > Add option to set when the perf buffer should wake up, by default the
> > perf buffer becomes signaled for every event that is being pushed to it.
> >
> > In case of a high throughput of events it will be more efficient to wake
> > up only once you have X events ready to be read.
> >
> > So your application can wakeup once and drain the entire perf buffer.
> >
> > Signed-off-by: Jon Doron <jond@xxxxxx>
> > ---
> > tools/lib/bpf/libbpf.c | 4 ++--
> > tools/lib/bpf/libbpf.h | 3 ++-
> > 2 files changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > index eed5cec6f510..6b30ff13922b 100644
> > --- a/tools/lib/bpf/libbpf.c
> > +++ b/tools/lib/bpf/libbpf.c
> > @@ -11719,8 +11719,8 @@ struct perf_buffer *perf_buffer__new(int map_fd, size_t page_cnt,
> > attr.config = PERF_COUNT_SW_BPF_OUTPUT;
> > attr.type = PERF_TYPE_SOFTWARE;
> > attr.sample_type = PERF_SAMPLE_RAW;
> > - attr.sample_period = 1;
> > - attr.wakeup_events = 1;
> > + attr.sample_period = OPTS_GET(opts, wakeup_events, 1);
> > + attr.wakeup_events = OPTS_GET(opts, wakeup_events, 1);
> >
> > p.attr = &attr;
> > p.sample_cb = sample_cb;
> > diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> > index 8777ff21ea1d..e83c0a915dc7 100644
> > --- a/tools/lib/bpf/libbpf.h
> > +++ b/tools/lib/bpf/libbpf.h
> > @@ -1246,8 +1246,9 @@ typedef void (*perf_buffer_lost_fn)(void *ctx, int cpu, __u64 cnt);
> > /* common use perf buffer options */
> > struct perf_buffer_opts {
> > size_t sz;
> > + __u32 wakeup_events;
>
> Since you are adding wakeup_events here, do you think it make sense
> to add sample_period to struct perf_buffer_opts as well? In some cases,
> users might want to have different values for sample_period and
> wakeup_events, e.g., smaller sample_period to accumulate data and
> larger wakeup_events to wakeup user space poll?
It's not clear to me from reading perf_event_open manpage what
"sample_period" means for perf buffer. What will happen when we have
sample_period != wakeup_events?
>
> > };
> > -#define perf_buffer_opts__last_field sz
> > +#define perf_buffer_opts__last_field wakeup_events
> >
> > /**
> > * @brief **perf_buffer__new()** creates BPF perfbuf manager for a specified
