linux-kernel - Re: [RFC PATCH bpf-next] libbpf: remove sample_period init in perf

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Message-ID: <aAfok3ha8QQkP8VB@google.com>
Date: Tue, 22 Apr 2025 12:05:55 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Jiri Olsa <olsajiri@...il.com>
Cc: Tao Chen <chen.dylane@...ux.dev>, andrii@...nel.org, eddyz87@...il.com,
	ast@...nel.org, daniel@...earbox.net, martin.lau@...ux.dev,
	song@...nel.org, yonghong.song@...ux.dev, john.fastabend@...il.com,
	kpsingh@...nel.org, sdf@...ichev.me, haoluo@...gle.com,
	bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH bpf-next] libbpf: remove sample_period init in
 perf_buffer

Hello,

On Tue, Apr 22, 2025 at 03:43:43PM +0200, Jiri Olsa wrote:
> On Tue, Apr 22, 2025 at 05:15:58PM +0800, Tao Chen wrote:
> > It seems that sample_period no used in perf buffer, actually only
> > wakeup_events valid about events aggregation for wakeup. So remove
> > it to avoid causing confusion.
> 
> I don't see too much confusion in keeping it, but I think it
> should be safe to remove it
> 
> PERF_COUNT_SW_BPF_OUTPUT is "trigered" by bpf_perf_event_output,
> AFAICS there's no path checking on sample_period for this event
> used in context of perf_buffer__new, Namhyung, thoughts?

It seems to be ok to call mmap(2) for non-sampling events.

Acked-by: Namhyung Kim <namhyung@...nel.org>

Thanks,
Namhyung

> 
> > 
> > Fixes: fb84b8224655 ("libbpf: add perf buffer API")
> > Signed-off-by: Tao Chen <chen.dylane@...ux.dev>
> > ---
> >  tools/lib/bpf/libbpf.c | 1 -
> >  1 file changed, 1 deletion(-)
> > 
> > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > index 194809da5172..1830e3c011a5 100644
> > --- a/tools/lib/bpf/libbpf.c
> > +++ b/tools/lib/bpf/libbpf.c
> > @@ -13306,7 +13306,6 @@ 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 = sample_period;
> >  	attr.wakeup_events = sample_period;
> >  
> >  	p.attr = &attr;
> > -- 
> > 2.43.0
> >