linux-kernel - Re: [RFC PATCH 5/6] bpf: Implement function bpf_read_pmu() that get the selected hardware PMU conuter

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Message-ID: <55A8EABE.1060308@huawei.com>
Date:	Fri, 17 Jul 2015 19:45:02 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	kaixu xia <xiakaixu@...wei.com>, <ast@...mgrid.com>,
	<davem@...emloft.net>, <acme@...nel.org>, <mingo@...hat.com>,
	<masami.hiramatsu.pt@...achi.com>, <jolsa@...nel.org>,
	<linux-kernel@...r.kernel.org>, <pi3orama@....com>,
	<hekuang@...wei.com>
Subject: Re: [RFC PATCH 5/6] bpf: Implement function bpf_read_pmu() that get
 the selected hardware PMU conuter



On 2015/7/17 19:39, Peter Zijlstra wrote:
> On Fri, Jul 17, 2015 at 07:29:07PM +0800, Wangnan (F) wrote:
>>
>> On 2015/7/17 19:05, Peter Zijlstra wrote:
>>> 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@...wei.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.
>> What about calling perf_event_read_value() then?
> Depends on what all you need, if you need full perf events to work then
> yes perf_event_read_value() is your only option.
>
> But note that that requires scheduling, so you cannot actually use it
> for tracing purposes etc..
What you mean "full perf events"? Even with your code some event still 
not work?

Thank you.

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