From: Huang Rui <ray.huang@amd.com>
To: Vince Weaver <vincent.weaver@maine.edu>
Cc: Borislav Petkov <bp@suse.de>,
Thomas Gleixner <tglx@linutronix.de>,
"Peter Zijlstra" <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
"Andy Lutomirski" <luto@amacapital.net>,
Robert Richter <rric@kernel.org>,
"Jacob Shin" <jacob.w.shin@gmail.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Kan Liang <kan.liang@intel.com>, <linux-kernel@vger.kernel.org>,
<x86@kernel.org>,
Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
Aravind Gopalakrishnan <Aravind.Gopalakrishnan@amd.com>,
Borislav Petkov <bp@alien8.de>,
Guenter Roeck <linux@roeck-us.net>,
Fengguang Wu <fengguang.wu@intel.com>
Subject: Re: [REDO PATCH v7] perf/x86/amd/power: Add AMD accumulated power reporting mechanism
Date: Thu, 16 Jun 2016 13:59:34 +0800 [thread overview]
Message-ID: <20160616055933.GA8522@hr-amur2> (raw)
In-Reply-To: <20160616053802.GA7810@hr-amur2>
On Thu, Jun 16, 2016 at 01:38:13PM +0800, Huang Rui wrote:
> On Wed, Jun 15, 2016 at 09:13:59PM -0400, Vince Weaver wrote:
> >
> > 2. Unless I'm misunderstanding things, the code seems to be accumulating
> > Power. (see chunk below) Power is an instantaneous measurement, it
> > makes no sense to add values. If you use 5W for 1ms and 10W for
> > 1ms, the average power across the 2ms interval is not 15W.
> >
> > You can add energy, but not power.
> >
> > > + delta *= cpu_pwr_sample_ratio * 1000;
> > > + tdelta = new_ptsc - prev_ptsc;
> > > +
> > > + do_div(delta, tdelta);
> > > + local64_add(delta, &event->count);
> >
>
> You're right. Nice catch! The average power is per compute unit. We
> cannot add the power simplely for each processor/package.
>
> So here, the average power per package should be (delta1 + delta2 + ... + deltaN)/(tdelta_avg).
> I will work out a fix. Thanks to point out.
>
After considering carefully, the original method should be OK.
AMD nomenclature for CMT systems:
[node 0] -> [Compute Unit 0] -> [Compute Unit Core 0] -> Linux CPU 0
-> [Compute Unit Core 1] -> Linux CPU 1
-> [Compute Unit 1] -> [Compute Unit Core 0] -> Linux CPU 2
-> [Compute Unit Core 1] -> Linux CPU 3
The deltaN is power per compute unit. Current one package has two CUs.
In the *same* interval, CU0's power is 10W, CU1's power is 15W. The
package (CU0 + CU1) power should be 15W, right? Because the interval
is the same.
Q = Q1 + Q2. P = Q/t = (Q1 + Q2)/t = Q1/t + Q2/t = P1 + P2.
Is that clear?
Thanks,
Rui
next prev parent reply other threads:[~2016-06-16 5:54 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-09 5:45 [REDO PATCH v7] perf/x86/amd/power: Add AMD accumulated power reporting mechanism Huang Rui
2016-03-21 9:55 ` [tip:perf/urgent] " tip-bot for Huang Rui
2016-06-16 1:13 ` [REDO PATCH v7] " Vince Weaver
2016-06-16 5:38 ` Huang Rui
2016-06-16 5:59 ` Huang Rui [this message]
2016-06-16 21:10 ` Vince Weaver
2016-06-16 21:16 ` Vince Weaver
2016-06-16 21:36 ` Borislav Petkov
2016-06-16 16:47 ` Borislav Petkov
2016-06-17 9:58 ` Huang Rui
2016-07-19 18:22 ` Vince Weaver
2016-07-20 2:58 ` Huang Rui
2016-06-16 20:44 ` Vince Weaver
2016-06-17 10:03 ` Huang Rui
2016-06-17 15:54 ` Vince Weaver
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