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

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Message-ID: <55E47E88.7080202@roeck-us.net>
Date:	Mon, 31 Aug 2015 09:19:20 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Borislav Petkov <bp@...en8.de>,
	Peter Zijlstra <peterz@...radead.org>
CC:	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 09:06 AM, Borislav Petkov wrote:
> On Mon, Aug 31, 2015 at 10:38:21AM +0200, Peter Zijlstra wrote:
>> 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
>
> Well, we can do finer-grained if needed. I'm all for everything which
> has a good use case. The use case we had in mind here was the physical
> processor power consumption for a time period.
>
>> -- which is all hwmon seems capable of.
>
> I guess we can do both - perf and hwmon. I don't see why not.
>
>> Not to mention the proposed code is horrible, who in their right mind
>> does two rdmsrl_safe_on_cpu() back to back.
>
> That's a good point - I missed that during previous review. Rui, please
> put the rdmsrl_safe_on_cpu() accesses in a separate function which you
> run on a particular CPU, for your next version.
>
... and maybe work with Peter to address the other hotplug related issues.

It might also be worthwhile thinking about per-CU attributes, if that
provides any value (Peter's comments suggested that this might be the case).

Thanks,
Guenter

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