linux-kernel - Re: [PATCH bpf-next 1/5] perf/core: Add PERF_FORMAT_LOST read

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Date:   Tue, 24 Sep 2019 10:33:42 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Daniel Xu <dxu@...uu.xyz>
Cc:     bpf@...r.kernel.org, songliubraving@...com, yhs@...com,
        andriin@...com, peterz@...radead.org, mingo@...hat.com,
        acme@...nel.org, ast@...com, alexander.shishkin@...ux.intel.com,
        namhyung@...nel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH bpf-next 1/5] perf/core: Add PERF_FORMAT_LOST read_format

On Tue, Sep 17, 2019 at 06:30:52AM -0700, Daniel Xu wrote:

SNIP

> +	PERF_FORMAT_MAX = 1U << 5,		/* non-ABI */
>  };
>  
>  #define PERF_ATTR_SIZE_VER0	64	/* sizeof first published struct */
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 0463c1151bae..ee08d3ed6299 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -1715,6 +1715,9 @@ static void __perf_event_read_size(struct perf_event *event, int nr_siblings)
>  	if (event->attr.read_format & PERF_FORMAT_ID)
>  		entry += sizeof(u64);
>  
> +	if (event->attr.read_format & PERF_FORMAT_LOST)
> +		entry += sizeof(u64);
> +
>  	if (event->attr.read_format & PERF_FORMAT_GROUP) {
>  		nr += nr_siblings;
>  		size += sizeof(u64);
> @@ -4734,6 +4737,24 @@ u64 perf_event_read_value(struct perf_event *event, u64 *enabled, u64 *running)
>  }
>  EXPORT_SYMBOL_GPL(perf_event_read_value);
>  
> +static struct pmu perf_kprobe;
> +static u64 perf_event_lost(struct perf_event *event)
> +{
> +	struct ring_buffer *rb;
> +	u64 lost = 0;
> +
> +	rcu_read_lock();
> +	rb = rcu_dereference(event->rb);
> +	if (likely(!!rb))
> +		lost += local_read(&rb->lost);
> +	rcu_read_unlock();
> +
> +	if (event->attr.type == perf_kprobe.type)
> +		lost += perf_kprobe_missed(event);

not sure what was the peterz's suggestion, but here you are mixing
ring buffer's lost count with kprobes missed count, seems wrong

maybe we could add PERF_FORMAT_KPROBE_MISSED

jirka