linux-kernel - Re: [PATCH v13 00/32] x86,fs/resctrl telemetry monitoring

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Message-ID: <aUH5QZ7_7WCRWY3Y@agluck-desk3>
Date: Tue, 16 Dec 2025 16:28:49 -0800
From: "Luck, Tony" <tony.luck@...el.com>
To: "Moger, Babu" <bmoger@....com>
CC: Fenghua Yu <fenghuay@...dia.com>, Reinette Chatre
	<reinette.chatre@...el.com>, Maciej Wieczor-Retman
	<maciej.wieczor-retman@...el.com>, Peter Newman <peternewman@...gle.com>,
	James Morse <james.morse@....com>, Babu Moger <babu.moger@....com>, "Drew
 Fustini" <dfustini@...libre.com>, Dave Martin <Dave.Martin@....com>, Chen Yu
	<yu.c.chen@...el.com>, <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	<patches@...ts.linux.dev>
Subject: Re: [PATCH v13 00/32] x86,fs/resctrl telemetry monitoring

On Wed, Nov 05, 2025 at 09:33:56AM -0600, Moger, Babu wrote:
> Hi Tony,
> 
> On 10/29/2025 1:59 PM, Luck, Tony wrote:
> > I took a stab at applying the AET patches on tob of Babu's v10
> > SDCIAE series https://lore.kernel.org/all/cover.1761090859.git.babu.moger@amd.com/
> > 
> > There are only a couple of easy to resolve conflicts.
> > 
> > I pushed a branch with v6.18-rc3 + SDCIAE + AET here:
> > 
> > git://git.kernel.org/pub/scm/linux/kernel/git/aegl/linux.git sdciae-aet
> > 
> 
> I ran your code on my AMD system. It appears to be working fine.
> I don't have the hardware that supports these features. It would be helpful
> to list the resctrl interface files (files in info directory and files each
> group) and give an example of how it looks in the system that supports these
> features. It can be in cover letter or resctrl.rst file as well. It will
> also help to review the code.

Reinette reminded me that I didn't provide the examples that I promised.

Here's what I plan to add to the v17 cover letter. Is this enough
detail?

-Tony

Examples:
--------

As with other resctrl monitoring features first create CTRL_MON or MON
directories and assign the tasks of interest to the group.

Energy events:
-------------

There are two events associated with energy consumption in the core.
The "core_energy" event reports out directly in Joules. To compute
power just take the difference between two samples and divide by the
time between them. E.g.

$ cat core_energy; sleep 10; cat core_energy
94499439.510380
94499607.019680
$ bc -q
scale=3
(94499607.019680 - 94499439.510380) / 10
16.750

So 16.75 Watts in this example.

Note that different runs of the same workload may report different
energy consumption. This happens when cores shift to different
voltage/frequency profiles due to overall system load.

The "activity" event reports energy usage in a manner independent
of voltage and frequency. This may be useful for developers to
assess how modifications to a program (e.g. attaching to a library
optimized to use AVX instructions) affect energy consumption. So
read the "activity" at the start and end of program execution and
compute the difference.

Perf events:
-----------

The other telemetry events largely duplicate events available using
"perf", but avoid of reading the perf counters on every context switch.
This may be a significant improvement when monitoring highly multi-threaded
applications. E.g. to find the ratio of core cycles to reference cycles:

$ cat unhalted_core_cycles unhalted_ref_cycles
1312249223146571
1660157011698276
$ { run application here }
$ cat unhalted_core_cycles unhalted_ref_cycles
1313573565617233
1661511224019444
$ bc -q
scale = 3
(1661511224019444 - 1660157011698276) / (1313573565617233 - 1312249223146571)
1.022