Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936879Ab3DJP27 (ORCPT ); Wed, 10 Apr 2013 11:28:59 -0400 Received: from mail-la0-f42.google.com ([209.85.215.42]:45478 "EHLO mail-la0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932799Ab3DJP25 (ORCPT ); Wed, 10 Apr 2013 11:28:57 -0400 MIME-Version: 1.0 In-Reply-To: <20130410125111.GA12923@gmail.com> References: <20130326140147.GB2029@redhat.com> <20130410125111.GA12923@gmail.com> Date: Wed, 10 Apr 2013 17:28:55 +0200 Message-ID: Subject: Re: [tip:sched/core] sched: Lower chances of cputime scaling overflow From: Frederic Weisbecker To: Ingo Molnar Cc: Stanislaw Gruszka , Peter Zijlstra , linux-kernel@vger.kernel.org, hpa@zytor.com, rostedt@goodmis.org, akpm@linux-foundation.org, tglx@linutronix.de, linux-tip-commits@vger.kernel.org, Linus Torvalds Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 898 Lines: 19 2013/4/10 Ingo Molnar : > > * Frederic Weisbecker wrote: > >> Of course 128 bits ops are very expensive, so to help you evaluating the >> situation, this is going to happen on every call to task_cputime_adjusted() and >> thread_group_adjusted(), namely: > > It's really only expensive for divisions. Addition and multiplication should be > straightforward and relatively low overhead, especially on 64-bit platforms. Ok, well we still have one division in the scaling path. I'm mostly worried about the thread group exit that makes use of it through threadgroup_cputime_adjusted(). Not sure if we can avoid that. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/