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

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Date:	Fri, 17 Jul 2015 19:29:07 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	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>, <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 19:05, 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?

   ...
   struct perf_event_context *ctx;
   u64 enabled, u64 running

   ctx = perf_event_ctx_lock(event);
   if (!event->state == PERF_EVENT_STATE_ERROR) {
     count = perf_event_read_value(event, &enable, &running);
   }
   perf_event_ctx_unlock(event, ctx);
   ...

Code is from perf_read().

Thank you.


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