linux-kernel - Re: [PATCH v3 2/3] bpf: Implement function bpf_perf_event_read() that get the selected hardware PMU conuter

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Date:	Mon, 3 Aug 2015 11:34:37 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Kaixu Xia <xiakaixu@...wei.com>
Cc:	ast@...mgrid.com, davem@...emloft.net, acme@...nel.org,
	mingo@...hat.com, masami.hiramatsu.pt@...achi.com,
	jolsa@...nel.org, wangnan0@...wei.com,
	linux-kernel@...r.kernel.org, pi3orama@....com, hekuang@...wei.com
Subject: Re: [PATCH v3 2/3] bpf: Implement function bpf_perf_event_read()
 that get the selected hardware PMU conuter

On Thu, Jul 23, 2015 at 09:42:41AM +0000, Kaixu Xia wrote:
> +static u64 bpf_perf_event_read(u64 r1, u64 index, u64 r3, u64 r4, u64 r5)
> +{
> +	struct bpf_map *map = (struct bpf_map *) (unsigned long) r1;
> +	struct bpf_array *array = container_of(map, struct bpf_array, map);
> +	struct perf_event *event;
> +
> +	if (index >= array->map.max_entries)
> +		return -E2BIG;
> +
> +	event = array->events[index];
> +	if (!event)
> +		return -EBADF;
> +
> +	if (event->state != PERF_EVENT_STATE_ACTIVE)
> +		return -ENOENT;
> +
> +	if (event->oncpu != raw_smp_processor_id() &&
> +	    event->ctx->task != current)
> +		return -EINVAL;
> +
> +	if (event->attr.inherit)
> +		return -EINVAL;
> +
> +	__perf_event_read(event);
> +
> +	return perf_event_count(event);
> +}

Please no poking of event internal state outside of perf code.
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