From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754527AbbGFLog (ORCPT ); Mon, 6 Jul 2015 07:44:36 -0400 Received: from casper.infradead.org ([85.118.1.10]:44869 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752715AbbGFLoe (ORCPT ); Mon, 6 Jul 2015 07:44:34 -0400 Date: Mon, 6 Jul 2015 13:44:30 +0200 From: Peter Zijlstra To: Afzal Mohammed Cc: linux-kernel@vger.kernel.org, Ingo Molnar Subject: Re: [PATCH] sched,fair: Remove > u32 weight handling for delta Message-ID: <20150706114430.GE3644@twins.programming.kicks-ass.net> References: <1436150677-1818-1-git-send-email-afzal.mohd.ma@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1436150677-1818-1-git-send-email-afzal.mohd.ma@gmail.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 06, 2015 at 08:14:37AM +0530, Afzal Mohammed wrote: > scaled down weight 'fact' would not be > u32 rather than unlikely as the > values being passed for delta is either NICE_O_LOAD or the weight of the > 'se' which would be a value that can be accomodated in a u32. This needs a bit more on why se->load.weight must fit u32 (its true, but not evident from this text). > Remove the initial > u32 handling on 'fact'. > > 9dbdb15553239 ("sched/fair: Rework sched_fair time accounting") in > addition to fixing the original issue of time moving backwards elsewhere > in the code, handled delta > u32 case (due to NO_HZ_FULL) which brought > in as it's part the change changed here. Because the unsigned long weight is a u64 on 64bit.. Now as long as we never call __calc_delta() on a rq weight -- which is a sum of weights and can indeed be larger than u32, we can indeed remove this. And I think we already assume such, see this story on why shift will remain positive. > The hunk being removed here > would not make a difference to it as this is on scaled weight > u32. > And pre-"9dbdb15553239" doesn't seem to have logical equivalent of hunk > removed here either. -ENOPARSE.