From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756250Ab2CMEru (ORCPT ); Tue, 13 Mar 2012 00:47:50 -0400 Received: from terminus.zytor.com ([198.137.202.10]:35223 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754654Ab2CMErs (ORCPT ); Tue, 13 Mar 2012 00:47:48 -0400 Date: Mon, 12 Mar 2012 21:47:29 -0700 From: tip-bot for Peter Zijlstra Message-ID: Cc: linux-kernel@vger.kernel.org, hpa@zytor.com, mingo@redhat.com, joe@perches.com, a.p.zijlstra@chello.nl, tglx@linutronix.de, mingo@elte.hu Reply-To: mingo@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org, joe@perches.com, a.p.zijlstra@chello.nl, tglx@linutronix.de, mingo@elte.hu In-Reply-To: <1331056466.11248.327.camel@twins> References: <1331056466.11248.327.camel@twins> To: linux-tip-commits@vger.kernel.org Subject: [tip:sched/core] sched: Update yield() docs Git-Commit-ID: 8e3fabfde445a872c8aec2296846badf24d7c8b4 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.6 (terminus.zytor.com [127.0.0.1]); Mon, 12 Mar 2012 21:47:35 -0700 (PDT) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 8e3fabfde445a872c8aec2296846badf24d7c8b4 Gitweb: http://git.kernel.org/tip/8e3fabfde445a872c8aec2296846badf24d7c8b4 Author: Peter Zijlstra AuthorDate: Tue, 6 Mar 2012 18:54:26 +0100 Committer: Ingo Molnar CommitDate: Mon, 12 Mar 2012 20:43:17 +0100 sched: Update yield() docs Suggested-by: Joe Perches Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/1331056466.11248.327.camel@twins Signed-off-by: Ingo Molnar --- kernel/sched/core.c | 20 ++++++++++++++++++-- 1 files changed, 18 insertions(+), 2 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 8781cec..47614a5 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4577,8 +4577,24 @@ EXPORT_SYMBOL(__cond_resched_softirq); /** * yield - yield the current processor to other threads. * - * This is a shortcut for kernel-space yielding - it marks the - * thread runnable and calls sys_sched_yield(). + * Do not ever use this function, there's a 99% chance you're doing it wrong. + * + * The scheduler is at all times free to pick the calling task as the most + * eligible task to run, if removing the yield() call from your code breaks + * it, its already broken. + * + * Typical broken usage is: + * + * while (!event) + * yield(); + * + * where one assumes that yield() will let 'the other' process run that will + * make event true. If the current task is a SCHED_FIFO task that will never + * happen. Never use yield() as a progress guarantee!! + * + * If you want to use yield() to wait for something, use wait_event(). + * If you want to use yield() to be 'nice' for others, use cond_resched(). + * If you still want to use yield(), do not! */ void __sched yield(void) {