Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751600AbaBMOtJ (ORCPT ); Thu, 13 Feb 2014 09:49:09 -0500 Received: from mail-lb0-f171.google.com ([209.85.217.171]:53588 "EHLO mail-lb0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751374AbaBMOtH (ORCPT ); Thu, 13 Feb 2014 09:49:07 -0500 MIME-Version: 1.0 In-Reply-To: <218b548b69479baa005af8a7b04a3abbea8ed6fa.1392252790.git.luto@amacapital.net> References: <20140212201709.GB6835@laptop.programming.kicks-ass.net> <218b548b69479baa005af8a7b04a3abbea8ed6fa.1392252790.git.luto@amacapital.net> Date: Thu, 13 Feb 2014 15:49:06 +0100 Message-ID: Subject: Re: [RFC] sched: Add a new lockless wake-from-idle implementation From: Frederic Weisbecker To: Andy Lutomirski Cc: Peter Zijlstra , Thomas Gleixner , Mike Galbraith , X86 ML , LKML 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 2014-02-13 2:40 GMT+01:00 Andy Lutomirski : > This is a strawman proposal to simplify the idle implementation, eliminate > a race Please describe the race in question. > > Benefits over current code: > - ttwu_queue_remote doesn't use an IPI unless needed > - The diffstat should speak for itself :) Actually referring to the diffstat alone sounds dangerous here. Sure this simplifies the code, I'm all for negative diffstat, and probably it avoids a few IPIs, but this comes at the cost of added non-cheap atomic_xchg() calls in some critical fastpath like resched_task() path, the timer enqueue path and the inner idle loop. So it's not like this all comes for free. I'm not saying we don't want it but at least some serious measurements is needed. -- 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/