From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752546AbcFIXD5 (ORCPT ); Thu, 9 Jun 2016 19:03:57 -0400 Received: from terminus.zytor.com ([198.137.202.10]:39612 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751880AbcFIXDz (ORCPT ); Thu, 9 Jun 2016 19:03:55 -0400 Date: Thu, 9 Jun 2016 16:03:41 -0700 From: tip-bot for Bjorn Helgaas Message-ID: Cc: mingo@kernel.org, john.stultz@linaro.org, hpa@zytor.com, bhelgaas@google.com, linux-kernel@vger.kernel.org, tglx@linutronix.de Reply-To: tglx@linutronix.de, linux-kernel@vger.kernel.org, bhelgaas@google.com, hpa@zytor.com, john.stultz@linaro.org, mingo@kernel.org In-Reply-To: <20160531212302.28502.44995.stgit@bhelgaas-glaptop2.roam.corp.google.com> References: <20160531212302.28502.44995.stgit@bhelgaas-glaptop2.roam.corp.google.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:timers/core] timers: Clarify usleep_range() function comment Git-Commit-ID: b5227d03b7191a9a44bf75a4c228a6a9ddbe781b 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 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: b5227d03b7191a9a44bf75a4c228a6a9ddbe781b Gitweb: http://git.kernel.org/tip/b5227d03b7191a9a44bf75a4c228a6a9ddbe781b Author: Bjorn Helgaas AuthorDate: Tue, 31 May 2016 16:23:02 -0500 Committer: Thomas Gleixner CommitDate: Fri, 10 Jun 2016 00:59:14 +0200 timers: Clarify usleep_range() function comment Update the usleep_range() function comment to make it clear that it can only be used in non-atomic context. Previously we claimed usleep_range() was a drop-in replacement for udelay() where wakeup is flexible. But that's only true in non-atomic contexts, where it's possible to sleep instead of delay. Signed-off-by: Bjorn Helgaas Cc: John Stultz Link: http://lkml.kernel.org/r/20160531212302.28502.44995.stgit@bhelgaas-glaptop2.roam.corp.google.com Signed-off-by: Thomas Gleixner --- kernel/time/timer.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/kernel/time/timer.c b/kernel/time/timer.c index 3a95f97..67dd610 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -1702,9 +1702,15 @@ static void __sched do_usleep_range(unsigned long min, unsigned long max) } /** - * usleep_range - Drop in replacement for udelay where wakeup is flexible + * usleep_range - Sleep for an approximate time * @min: Minimum time in usecs to sleep * @max: Maximum time in usecs to sleep + * + * In non-atomic context where the exact wakeup time is flexible, use + * usleep_range() instead of udelay(). The sleep improves responsiveness + * by avoiding the CPU-hogging busy-wait of udelay(), and the range reduces + * power usage by allowing hrtimers to take advantage of an already- + * scheduled interrupt instead of scheduling a new one just for this sleep. */ void __sched usleep_range(unsigned long min, unsigned long max) {