linux-kernel - Re: [PATCH] perf: add /proc/perf_events file for dump perf events info

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Date:	Thu, 5 Jul 2012 21:38:46 +0800
From:	Jovi Zhang <bookjovi@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf: add /proc/perf_events file for dump perf events info

On Thu, Jul 5, 2012 at 9:08 PM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> On Thu, 2012-07-05 at 21:02 +0800, Jovi Zhang wrote:
>> > Watch all perf events in system wide can be very useful for perf subsystem issue handling,
>> > to know which perf event is active in system,
>> > perf event is a resouce, it would like to be managed easily for user, with more visable, like /proc/timer, etc...
>> >
>> > .jovi
>>
>>
>> Ping...
>
> Never saw your reply, due to HTML it landed in the spam folder.
>
> That's a pretty non-specific answer.. again, why are you interested,
> what specific problem are you wanting to solve.
>
> I've never had this need myself.
>
sorry, I will try to explain more.

One problem I faced is about hw_breakpoint.
As you known, hw_breakpoint use limit debug register in most architecture,
In multi-user environment, sometime user cannot set hw_breakpoint because
other user already occupy hw_breakpoint slots. currently, there don't
have a way to know
how many hw_breakpint perf event already is used in system, so that's
why I thinking
we might need a way to get perf event in systerm wide, with visable output.

Also this method is not only used for hw_breakpoint, others perf event
might have similar problem,
even other perf event don't have limit number, but it can make use of
this /proc/perf_events

Active perf events is cpu consumer at most time, at this point of
view, system administrator also can use this
/proc/perf_events to detect is there have any perf events is consuming cpu.

A method to detect perf event leak? of couse our perf subsystem is
very stable right now, ingnore this :)

.jovi
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