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

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Message-ID: <aAkMbBdzWX_iE1zM@krava>
Date: Wed, 23 Apr 2025 17:51:08 +0200
From: Jiri Olsa <olsajiri@...il.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Jiri Olsa <olsajiri@...il.com>, 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

On Tue, Apr 22, 2025 at 12:05:55PM -0700, Namhyung Kim wrote:
> 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>

Tao Chen,
could you please resend without rfc tag? plz keeps acks

Acked-by: Jiri Olsa <jolsa@...nel.org>

thanks,
jirka


> 
> 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
> > >