linux-kernel - [RFC/PATCH 0/2] powernv:cpuidle: Enable winkle idle state

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Date:   Fri, 19 Aug 2016 03:56:53 +0530
From:   "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Michael Neuling <michael.neuling@....ibm.com>,
        Paul Mackerras <paulus@...ba.org>,
        Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
Cc:     Anton Blanchard <anton@...ba.org>, linux-pm@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
Subject: [RFC/PATCH 0/2] powernv:cpuidle: Enable winkle idle state

From: "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>

Hi,

The patches in these series enable support for Winkle idle state in
CPU-Idle.

The first patch is a platform-independent CPU-Idle patch that allows
CPU-Idle states to be  disabled at start (Currently they are all
enabled by default).

The second patch adds the winkle enablement for powernv-cpuidle. By
default, the winkle idle-state is disabled. It can be enabled by
writing zero to the per-cpu cpuidle sysfs control file named
"disable".

This series has been lightly tested on a 2-socket POWER8 system and
the machine was pretty stable while running kernbench and ebizzy. I
didn't see any regressions with those.

I haven't yet evaluated the impact that these patches might have
on latency sensitive workloads. I hope to do that in a day or two.

On the power-savings front, I could observe 6-8% additional
power-savings when winkle state was enabled on an idle system with
SMT=on. With SMT=off, additional idle power-savings observed with
winkle enabled were greater than 15%.  The numbers indicate that it
might be worth the while to pursue this!

Gautham R. Shenoy (2):
  cpuidle: Allow idle-states to be disabled at start
  powernv:cpuidle: Enable winkle idle state in CPU-Idle.

 drivers/cpuidle/cpuidle-powernv.c | 44 ++++++++++++++++++++++++++++++++-------
 drivers/cpuidle/cpuidle.c         |  7 +++++++
 include/linux/cpuidle.h           |  7 ++++++-
 3 files changed, 49 insertions(+), 9 deletions(-)

-- 
1.9.4