Date: Fri, 17 Jul 2015 13:05:41 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: kaixu xia <xiakaixu@huawei.com>
Cc: ast@plumgrid.com, davem@davemloft.net, acme@kernel.org, mingo@redhat.com,
        masami.hiramatsu.pt@hitachi.com, jolsa@kernel.org, wangnan0@huawei.com,
        linux-kernel@vger.kernel.org, pi3orama@163.com, hekuang@huawei.com
Subject: Re: [RFC PATCH 5/6] bpf: Implement function bpf_read_pmu() that get
 the selected hardware PMU conuter
Message-ID: <20150717110541.GJ12596@twins.programming.kicks-ass.net>
References: <1437129816-13176-1-git-send-email-xiakaixu@huawei.com>
 <1437129816-13176-6-git-send-email-xiakaixu@huawei.com>
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On Fri, Jul 17, 2015 at 06:43:35PM +0800, kaixu xia wrote:
> The function bpf_read_pmu() can get the specific map key, convert
> the corresponding map value to the pointer to struct perf_event and
> return the Hardware PMU counter value.

Thanks for having me on Cc :/

> Signed-off-by: kaixu xia <xiakaixu@huawei.com>
> ---
> +static u64 bpf_read_pmu(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
> +{
> +	void *value = (void *) (unsigned long) r1;
> +	struct perf_event *event;
> +	u64 count;
> +
> +	if (!value || !(*(unsigned long *)value))
> +		return 0;
> +
> +	event = (struct perf_event *)(*(unsigned long *)value);
> +
> +	if (event->state == PERF_EVENT_STATE_ACTIVE)
> +		event->pmu->read(event);
> +
> +	count = local64_read(&event->count);
> +
> +	return count;
> +}

Hell no, that's way broken.
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