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: <20150717115505.GF19282@twins.programming.kicks-ass.net>
Date:	Fri, 17 Jul 2015 13:55:05 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Wangnan (F)" <wangnan0@...wei.com>
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 Fri, Jul 17, 2015 at 07:45:02PM +0800, Wangnan (F) wrote:

> >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?

The code I posted only works for events that do not have inherit set.
And only works from IRQ/NMI context for events that monitor the current
task or the current CPU (although that needs a little extra code still).

Anything else and it does not work (correctly).
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