Re: [PATCH bpf-next v1] libbpf: Add wakeup_events to creation options

[Jiri Olsa <olsajiri@gmail.com>]

On Wed, Feb 01, 2023 at 11:00:09AM +0200, Jon Doron wrote:
> From: Jon Doron <jond@wiz.io>
> 
> 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@wiz.io>
> ---
>  tools/lib/bpf/libbpf.c | 4 ++--
>  tools/lib/bpf/libbpf.h | 1 +
>  2 files changed, 3 insertions(+), 2 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);

hm, but I think we still want every event.. setting sample_period to X
would store only every X-th bpf-output event, no?

jirka

> +	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..2e4bdfc58c82 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -1246,6 +1246,7 @@ 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;
>  };
>  #define perf_buffer_opts__last_field sz
>  
> -- 
> 2.39.1
>