linux-kernel - Re: [PATCH 09/15] x86, amd: add accessor for number of cores per compute unit

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Message-ID: <55E45C76.3070704@roeck-us.net>
Date:	Mon, 31 Aug 2015 06:53:58 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...nel.org>,
	Huang Rui <ray.huang@....com>, Borislav Petkov <bp@...e.de>,
	Jean Delvare <jdelvare@...e.de>,
	Andy Lutomirski <luto@...capital.net>,
	Andreas Herrmann <herrmann.der.user@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <lenb@...nel.org>,
	John Stultz <john.stultz@...aro.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	lm-sensors@...sensors.org, linux-kernel@...r.kernel.org,
	x86@...nel.org,
	Andreas Herrmann <herrmann.der.user@...glemail.com>,
	Aravind Gopalakrishnan <Aravind.Gopalakrishnan@....com>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Aaron Lu <aaron.lu@...el.com>, Tony Li <tony.li@....com>
Subject: Re: [PATCH 09/15] x86, amd: add accessor for number of cores per
 compute unit

On 08/31/2015 06:38 AM, Peter Zijlstra wrote:
> On Mon, Aug 31, 2015 at 06:26:00AM -0700, Guenter Roeck wrote:
>> On 08/31/2015 01:38 AM, Peter Zijlstra wrote:
>>> On Sun, Aug 30, 2015 at 05:53:22PM +0200, Borislav Petkov wrote:
>>>> On Sat, Aug 29, 2015 at 11:19:14AM +0200, Ingo Molnar wrote:
>>>>> So let me withdraw my ack: the much more important question that I
>>>>> missed first time around, why is this reporting feature living in
>>>>> hwmon, not in perf? We have energy reporting facilities in perf that
>>>>> this should be synced to.
>>>>
>>>> Because there's already fam15h_power driver which is exactly for that.
>>>> Making it part of perf is then a question of cat-ting the same sysfs
>>>> file twice, at the beginning and at the end of the trace, which is
>>>> trivial.
>>>
>>> That don't make sense.
>>>
>>> Looking at the BKDG Fam 15h 60h-6Fh these MSRs are per compute unit.
>>> This means you can do much finer grained measurements than system wide
>>> -- which is all hwmon seems capable of.
>>>
>>
>> Is it ? Why ?
>
> Dunno, because there's that big old loop iterating all cpus?
>

What does that have to do with 'hwmon' ? The current implementation in the
driver may not be a good idea, and maybe for good reasons; I can not
comment on that. However, you concluded from that implementation that
hwmon, the subsystem, would not be able to support 'much finer grained
measurements than system wide'. I would like to understand how you reached
that conclusion.

Thanks,
Guenter

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