linux-kernel - Re: [Results] [RFC PATCH v4 00/40] mm: Memory Power Management

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Date:	Tue, 12 Nov 2013 09:34:33 -0800
From:	Dave Hansen <dave@...1.net>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	mgorman@...e.de, hannes@...xchg.org, tony.luck@...el.com,
	matthew.garrett@...ula.com, riel@...hat.com, arjan@...ux.intel.com,
	srinivas.pandruvada@...ux.intel.com, willy@...ux.intel.com,
	kamezawa.hiroyu@...fujitsu.com, lenb@...nel.org, rjw@...k.pl,
	gargankita@...il.com, paulmck@...ux.vnet.ibm.com,
	svaidy@...ux.vnet.ibm.com, andi@...stfloor.org,
	isimatu.yasuaki@...fujitsu.com, santosh.shilimkar@...com,
	kosaki.motohiro@...il.com, linux-pm@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	maxime.coquelin@...ricsson.com, loic.pallardy@...ricsson.com,
	amit.kachhap@...aro.org, thomas.abraham@...aro.org,
	markgross@...gnar.org
Subject: Re: [Results] [RFC PATCH v4 00/40] mm: Memory Power Management

On 11/12/2013 12:02 AM, Srivatsa S. Bhat wrote:
> I performed experiments on an IBM POWER 7 machine and got actual power-savings
> numbers (upto 2.6% of total system power) from this patchset. I presented them
> at the Kernel Summit but forgot to post them on LKML. So here they are:

"upto"?  What was it, actually?  Essentially what you've told us here is
that you have a patch that tries to do some memory power management and
that it accomplishes that.  But, to what degree?

Was your baseline against a kernel also booted with numa=fake=1, or was
it a kernel booted normally?

1. What is the theoretical power savings from memory?
2. How much of the theoretical numbers can your patch reach?
3. What is the performance impact?  Does it hurt ebizzy?

You also said before:
> On page 40, the paper shows the power-consumption breakdown for an IBM p670
> machine, which shows that as much as 40% of the system energy is consumed by
> the memory sub-system in a mid-range server.

2.6% seems pretty awful for such an invasive patch set if you were
expecting 40%.
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