From: Peter Zijlstra <peterz@infradead.org>
To: Andy Lutomirski <luto@amacapital.net>
Cc: "Brown, Len" <len.brown@intel.com>,
Andy Lutomirski <luto@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Paul Mackerras <paulus@samba.org>, Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>
Subject: Re: [RFC] x86, perf: Add an aperfmperf driver
Date: Wed, 29 Apr 2015 11:13:05 +0200 [thread overview]
Message-ID: <20150429091305.GP5029@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <CALCETrXQGWWAc+yYFrmHKiVAHVxPK37M2La1Q2k51xzAffbpHg@mail.gmail.com>
On Tue, Apr 28, 2015 at 03:43:38PM -0700, Andy Lutomirski wrote:
> On Tue, Apr 28, 2015 at 3:29 PM, Brown, Len <len.brown@intel.com> wrote:
> >> Thoughts? Would it make sense at all? Did I wire it up right? This is
> >> the only PMU driver I've ever written, and it could have any number of
> >> issues.
> >
> > APERF/MPERF, as with all per-thread MSRs, must be accessed
> > from the local processor. I didn't see where this driver
> > distinguishes the CPU. Also, I assume the intent is to return
> > a snapshot, rather than sampling, yes?
>
> I think that the perf core takes care of that for us, but I'm not entirely sure.
It does indeed. The events are always created/used in either task or cpu
context, and in the case of task context they're context switched along,
which again results in strict per cpu usage.
Since this driver has no state to track nothing else is required.
next prev parent reply other threads:[~2015-04-29 9:13 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-28 21:25 [RFC] x86, perf: Add an aperfmperf driver Andy Lutomirski
2015-04-28 22:29 ` Brown, Len
2015-04-28 22:43 ` Andy Lutomirski
2015-04-29 9:13 ` Peter Zijlstra [this message]
2015-04-29 9:09 ` Peter Zijlstra
2015-04-29 18:50 ` Andy Lutomirski
2015-04-30 1:17 ` Andy Lutomirski
2015-04-30 8:51 ` Peter Zijlstra
2015-04-30 22:09 ` Andy Lutomirski
2015-04-29 9:14 ` Peter Zijlstra
2015-05-11 9:48 ` Ingo Molnar
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