From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1753696AbcD1Jp7 (ORCPT <rfc822;w@1wt.eu>);
	Thu, 28 Apr 2016 05:45:59 -0400
Received: from mail-wm0-f68.google.com ([74.125.82.68]:32870 "EHLO
	mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1753464AbcD1Jpw (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Thu, 28 Apr 2016 05:45:52 -0400
Date: Thu, 28 Apr 2016 11:45:48 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Yuyang Du <yuyang.du@intel.com>, linux-kernel@vger.kernel.org,
        bsegall@google.com, pjt@google.com, morten.rasmussen@arm.com,
        vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
        lizefan@huawei.com, umgwanakikbuti@gmail.com
Subject: Re: [PATCH v3 6/6] sched/fair: Move (inactive) option from code to
 config
Message-ID: <20160428094548.GA23387@gmail.com>
References: <1459829551-21625-1-git-send-email-yuyang.du@intel.com>
 <1459829551-21625-7-git-send-email-yuyang.du@intel.com>
 <20160428093733.GX3430@twins.programming.kicks-ass.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20160428093733.GX3430@twins.programming.kicks-ass.net>
User-Agent: Mutt/1.5.23 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


* Peter Zijlstra <peterz@infradead.org> wrote:

> On Tue, Apr 05, 2016 at 12:12:31PM +0800, Yuyang Du wrote:
> > The option of increased load resolution (fixed point arithmetic range) is
> > unconditionally deactivated with #if 0. But since it may still be used
> > somewhere (e.g., in Google), we want to keep this option.
> > 
> > Regardless, there should be a way to express this option. Considering the
> > current circumstances, the reconciliation is we define a config
> > CONFIG_CFS_INCREASE_LOAD_RANGE and it depends on FAIR_GROUP_SCHED and
> > 64BIT and BROKEN.
> > 
> > Suggested-by: Ingo Molnar <mingo@kernel.org>
> 
> So I'm very tempted to simply, unconditionally, reinstate this larger
> range for everything CONFIG_64BIT && CONFIG_FAIR_GROUP_SCHED.
> 
> There was but the single claim on increased power usage, nobody could
> reproduce / analyze and Google has been running with this for years now.
> 
> Furthermore, it seems to be leading to the obvious problems on bigger
> machines where we basically run out of precision by the sheer number of
> cpus (nr_cpus ~ SCHED_LOAD_SCALE and stuff comes apart quickly).

Agreed.

Thanks,

	Ingo