linux-kernel - Re: [PATCH v5 2/6] hwmon: (fam15h_power) Add compute unit accumulated power

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Date:	Tue, 29 Mar 2016 09:57:49 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Huang Rui <ray.huang@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Guenter Roeck <linux@...ck-us.net>,
	Jean Delvare <jdelvare@...e.de>, linux-hwmon@...r.kernel.org,
	linux-kernel@...r.kernel.org, spg_linux_kernel@....com
Subject: Re: [PATCH v5 2/6] hwmon: (fam15h_power) Add compute unit
 accumulated power

On Tue, Mar 29, 2016 at 09:31:58AM +0200, Peter Zijlstra wrote:
> This will not in fact work for Intel, nor if I manage to one day
> randomize our CPU numbers on AMD.

Oh, I know why. I have this 64 CPUs box here:

$ grep "core id" /proc/cpuinfo | uniq
core id         : 0
core id         : 8
core id         : 2
core id         : 10
core id         : 1
core id         : 9
core id         : 3
core id         : 11
core id         : 0
core id         : 8
core id         : 2
core id         : 10
core id         : 1
core id         : 9
core id         : 3
core id         : 11

Those core IDs repeat and are almost random too :)

I guess we'll need a mask. Maybe as a future exercise...

That box's topology has other funsies like this:

$ grep -E -B 2 "core id\s+: 0" /proc/cpuinfo
physical id     : 0
siblings        : 16
core id         : 0
--
physical id     : 1
siblings        : 16
core id         : 0
--
physical id     : 2
siblings        : 16
core id         : 0
--
physical id     : 3
siblings        : 16
core id         : 0
--
physical id     : 0
siblings        : 16
core id         : 0
--
physical id     : 1
siblings        : 16
core id         : 0
--
physical id     : 2
siblings        : 16
core id         : 0
--
physical id     : 3
siblings        : 16
core id         : 0

So in order to dig out which HT threads belong together, I need to look
at the (core id, physical id) pair.

I guess this is how we "fix" the schedulers of other OSes - by playing
topology games...

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.