From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755134Ab1I2O73 (ORCPT ); Thu, 29 Sep 2011 10:59:29 -0400 Received: from mx1.redhat.com ([209.132.183.28]:1034 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751204Ab1I2O72 (ORCPT ); Thu, 29 Sep 2011 10:59:28 -0400 From: Matthew Garrett To: tglx@linutronix.de Cc: linux-kernel@vger.kernel.org, arjan@infradead.org, Matthew Garrett Subject: [PATCH] hrtimers: Special-case zero length sleeps Date: Thu, 29 Sep 2011 10:59:32 -0400 Message-Id: <1317308372-6810-1-git-send-email-mjg@redhat.com> X-SA-Do-Not-Run: Yes X-SA-Exim-Connect-IP: 66.187.233.202 X-SA-Exim-Mail-From: mjg@redhat.com X-SA-Exim-Scanned: No (on cavan.codon.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org sleep(0) is a common construct used by applications that want to trigger the scheduler. sched_yield() might make more sense, but only appeared in POSIX.1-2001 and so plenty of example code still uses the sleep(0) form. This wouldn't normally be a problem, but it means that event-driven applications that are merely trying to avoid starving other processes may actually end up sleeping due to having large timer_slack values. Special- casing this seems reasonable. Signed-off-by: Matthew Garrett --- kernel/hrtimer.c | 8 ++++++++ 1 files changed, 8 insertions(+), 0 deletions(-) diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c index a9205e3..0bb70a7 100644 --- a/kernel/hrtimer.c +++ b/kernel/hrtimer.c @@ -1566,6 +1566,14 @@ long hrtimer_nanosleep(struct timespec *rqtp, struct timespec __user *rmtp, if (rt_task(current)) slack = 0; + /* + * Applications will often sleep(0) to indicate that they wish to + * be scheduled. Special case that to avoid actually putting them + * to sleep for the duration of the slack. + */ + if (rqtp->tv_sec == 0 && rqtp->tv_nsec == 0) + slack = 0; + hrtimer_init_on_stack(&t.timer, clockid, mode); hrtimer_set_expires_range_ns(&t.timer, timespec_to_ktime(*rqtp), slack); if (do_nanosleep(&t, mode)) -- 1.7.6.4