From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752420AbcF1ITC (ORCPT ); Tue, 28 Jun 2016 04:19:02 -0400 Received: from mailout3.samsung.com ([203.254.224.33]:41018 "EHLO mailout3.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752332AbcF1IS5 (ORCPT ); Tue, 28 Jun 2016 04:18:57 -0400 X-AuditID: cbfee61a-f79106d000000835-08-577232e11af6 From: Bartlomiej Zolnierkiewicz To: Nicolas Pitre Cc: Lorenzo Pieralisi , Russell King , Viresh Kumar , Sudeep Holla , Dave Martin , Sudeep KarkadaNagesha , "Rafael J. Wysocki" , Thomas Gleixner , Jason Cooper , Marc Zyngier , Krzysztof Kozlowski , linux-arm-kernel@lists.infradead.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 0/4] ARM: remove big.LITTLE switcher support Date: Tue, 28 Jun 2016 10:18:17 +0200 Message-id: <8154264.t0CjdgHDuf@amdc1976> User-Agent: KMail/4.13.3 (Linux/3.13.0-79-generic; KDE/4.13.3; x86_64; ; ) In-reply-to: References: <1467026770-5699-1-git-send-email-b.zolnierkie@samsung.com> MIME-version: 1.0 Content-transfer-encoding: 7Bit Content-type: text/plain; charset=us-ascii X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFprGIsWRmVeSWpSXmKPExsVy+t9jQd2HRkXhBvO2GVv8X7yeyaJxyWUW i9cvDC02Pb7GanF51xw2i8+9Rxgt3vx+wW7x984/NotPz/6xW5w5fYnVYvOHl2wWy0/tYLG4 9nwXs8XmTVOZLTZ+9XDg91gzbw2jR0tzD5tHw4HzLB53ru1h83h37hy7x+Yl9R5brrazePRt WcXo8XmTXABnFJdNSmpOZllqkb5dAlfGg+6VbAUT+SsWLfFpYPzF3cXIwSEhYCJxfqNBFyMn kCkmceHeerYuRi4OIYFZjBKPjj5mB0kICXxllJh2JB3EZhOwkpjYvooRxBYR0JE4OvM1M0gD s8B+Fok5b9+xgCSEBVwkOv+0s4HYLAKqEg3nzjOB2LwCmhKPrtwGi4sKeEn0bH8ENohTwFai /+UlZohlVRLPdkxnh6gXlPgx+R7YTGYBeYl9+6eyQthaEut3HmeawAh0JkLZLCRls5CULWBk XsUokVqQXFCclJ5rmJdarlecmFtcmpeul5yfu4kRHFvPpHYwHtzlfohRgINRiYd3R11huBBr YllxZe4hRgkOZiUR3pd6ReFCvCmJlVWpRfnxRaU5qcWHGKU5WJTEeR//XxcmJJCeWJKanZpa kFoEk2Xi4JRqYFSS6+89yxrItUns+kXXHxdms9jaPxEvq19y+difJu+7p1n/LTuoGRn5QNzw ldl2pvkd0hzBKuk3/VX+aXVx+uRM3trDyS18eMOGuwphu/mv1Dpy6Nv//Xz+XuaZZY/lbG3V Fh6fWLus56lSit/EG1tFvSQq3m/U0XZ9Gr89iOmle5nowTclv5RYijMSDbWYi4oTAVDskOOp AgAA Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On Monday, June 27, 2016 03:49:44 PM Nicolas Pitre wrote: > On Mon, 27 Jun 2016, Bartlomiej Zolnierkiewicz wrote: > > > Hi, > > > > It seems that in mainline kernel big.LITTLE switcher support > > may be usable only on ARM Versatile Express TC2 platform > > (but even this platform doesn't enable it in its defconfig). > > It is also used on some Samsung targets. Could you please explain this more? AFAIK mainline never had working IKS solution (big.LITTLE switcher support + arm_big_little CPUfreq driver support) on any Samsung SoC. > > The following patchset removes big.LITTLE switcher support > > (from both ARM core and arm_big_little CPUfreq driver) in > > favor of using HMP. > > > > Since HMP support at scheduler level is not yet merged this > > patchset is probably premature and thus is marked as RFC. > > It is premature indeed. > > And before this is removed, comparison with power/performance benchmark > numbers will have to be provided as well to justify this removal. At > the moment there is nothing else in mainline that can achieve what this > code does. I agree given that this code has real users and according to my research on mainline kernel it seems that the IKS functionality (bL switcher core code together with arm_bit_little CPUfreq driver support) is usable only on TC2 and even this platform doesn't enable it by default. IOW I would really like to get the confirmation that there are platforms that are making use of IKS functionality currently with the mainline kernel. Otherwise we should either consider its removal or enable it on platforms that are supposed to use it. > We all agree that the scheduler based solution is the best way to do it. > But this has been a couple years already and this is still work in > progress. Best regards, -- Bartlomiej Zolnierkiewicz Samsung R&D Institute Poland Samsung Electronics