From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751914Ab3LLOVP (ORCPT ); Thu, 12 Dec 2013 09:21:15 -0500 Received: from merlin.infradead.org ([205.233.59.134]:36004 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751474Ab3LLOVM (ORCPT ); Thu, 12 Dec 2013 09:21:12 -0500 Message-Id: <20131212141655.485306919@infradead.org> User-Agent: quilt/0.60-1 Date: Thu, 12 Dec 2013 15:08:50 +0100 From: Peter Zijlstra To: Arjan van de Ven , lenb@kernel.org, rjw@rjwysocki.net, Eliezer Tamir , rui.zhang@intel.com, jacob.jun.pan@linux.intel.com, Mike Galbraith , Ingo Molnar , hpa@zytor.com, paulmck@linux.vnet.ibm.com, Thomas Gleixner , John Stultz , Andy Lutomirski , Peter Zijlstra Cc: linux-kernel@vger.kernel.org Subject: [PATCH 15/15] x86: Avoid a runtime condition in native_sched_clock() References: <20131212140835.729222186@infradead.org> Content-Disposition: inline; filename=peterz-tsc-static_key.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Use a static_key to avoid touching tsc_disabled and a runtime condition in native_sched_clock() -- less cachelines touched is always better. MAINLINE PRE POST sched_clock_stable: 1 1 1 (cold) sched_clock: 329841 215295 213039 (cold) local_clock: 301773 220773 216084 (warm) sched_clock: 38375 25659 25231 (warm) local_clock: 100371 27242 27601 (warm) rdtsc: 27340 24208 24203 sched_clock_stable: 0 0 0 (cold) sched_clock: 382634 237019 240055 (cold) local_clock: 396890 294819 299942 (warm) sched_clock: 38194 25609 25276 (warm) local_clock: 143452 71232 73232 (warm) rdtsc: 27345 24243 24244 Signed-off-by: Peter Zijlstra --- arch/x86/kernel/tsc.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -11,6 +11,7 @@ #include #include #include +#include #include #include @@ -37,6 +38,8 @@ static int __read_mostly tsc_unstable; erroneous rdtsc usage on !cpu_has_tsc processors */ static int __read_mostly tsc_disabled = -1; +static struct static_key __use_tsc = STATIC_KEY_INIT; + int tsc_clocksource_reliable; /* @@ -243,7 +246,7 @@ u64 native_sched_clock(void) * very important for it to be as fast as the platform * can achieve it. ) */ - if (unlikely(tsc_disabled)) { + if (!static_key_false(&__use_tsc)) { /* No locking but a rare wrong value is not a big deal: */ return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ); } @@ -1152,7 +1155,9 @@ void __init tsc_init(void) return; /* now allow native_sched_clock() to use rdtsc */ + tsc_disabled = 0; + static_key_slow_inc(&__use_tsc); if (!no_sched_irq_time) enable_sched_clock_irqtime();