From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753517AbaGPVIb (ORCPT ); Wed, 16 Jul 2014 17:08:31 -0400 Received: from www.linutronix.de ([62.245.132.108]:59887 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753201AbaGPVFN (ORCPT ); Wed, 16 Jul 2014 17:05:13 -0400 Message-Id: <20140716205056.964226252@linutronix.de> User-Agent: quilt/0.63-1 Date: Wed, 16 Jul 2014 21:05:12 -0000 From: Thomas Gleixner To: LKML Cc: John Stultz , Peter Zijlstra Subject: [patch V2 56/64] clocksource: Move cycle_last validation to core code References: <20140716205018.175419210@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Disposition: inline; filename=clocksource-move-cycle_last-validation-to-core.patch X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The only user of the cycle_last validation is the x86 TSC. In order to provide NMI safe accessor functions for clock monotonic and monotonic_raw we need to do that in the core. We can't do the TSC specific if (now < cycle_last) now = cycle_last; for the other wrapping around clocksources, but TSC has CLOCKSOURCE_MASK(64) which actually does not mask out anything so if now is less than cycle_last the subtraction will give a negative result. So we can check for that in clocksource_delta() and return 0 for that case. Implement and enable it for x86 Signed-off-by: Thomas Gleixner --- arch/x86/Kconfig | 1 + arch/x86/kernel/tsc.c | 21 +++++++++------------ kernel/time/Kconfig | 5 +++++ kernel/time/timekeeping_internal.h | 9 +++++++++ 4 files changed, 24 insertions(+), 12 deletions(-) Index: tip/arch/x86/Kconfig =================================================================== --- tip.orig/arch/x86/Kconfig +++ tip/arch/x86/Kconfig @@ -109,6 +109,7 @@ config X86 select CLOCKSOURCE_WATCHDOG select GENERIC_CLOCKEVENTS select ARCH_CLOCKSOURCE_DATA + select CLOCKSOURCE_VALIDATE_LAST_CYCLE select GENERIC_CLOCKEVENTS_BROADCAST if X86_64 || (X86_32 && X86_LOCAL_APIC) select GENERIC_TIME_VSYSCALL select GENERIC_STRNCPY_FROM_USER Index: tip/arch/x86/kernel/tsc.c =================================================================== --- tip.orig/arch/x86/kernel/tsc.c +++ tip/arch/x86/kernel/tsc.c @@ -951,7 +951,7 @@ core_initcall(cpufreq_tsc); static struct clocksource clocksource_tsc; /* - * We compare the TSC to the cycle_last value in the clocksource + * We used to compare the TSC to the cycle_last value in the clocksource * structure to avoid a nasty time-warp. This can be observed in a * very small window right after one CPU updated cycle_last under * xtime/vsyscall_gtod lock and the other CPU reads a TSC value which @@ -961,26 +961,23 @@ static struct clocksource clocksource_ts * due to the unsigned delta calculation of the time keeping core * code, which is necessary to support wrapping clocksources like pm * timer. + * + * This sanity check is now done in the core timekeeping code. + * checking the result of read_tsc() - cycle_last for being negative. + * That works because CLOCKSOURCE_MASK(64) does not mask out any bit. */ static cycle_t read_tsc(struct clocksource *cs) { - cycle_t ret = (cycle_t)get_cycles(); - - return ret >= clocksource_tsc.cycle_last ? - ret : clocksource_tsc.cycle_last; -} - -static void resume_tsc(struct clocksource *cs) -{ - if (!boot_cpu_has(X86_FEATURE_NONSTOP_TSC_S3)) - clocksource_tsc.cycle_last = 0; + return (cycle_t)get_cycles(); } +/* + * .mask MUST be CLOCKSOURCE_MASK(64). See comment above read_tsc() + */ static struct clocksource clocksource_tsc = { .name = "tsc", .rating = 300, .read = read_tsc, - .resume = resume_tsc, .mask = CLOCKSOURCE_MASK(64), .flags = CLOCK_SOURCE_IS_CONTINUOUS | CLOCK_SOURCE_MUST_VERIFY, Index: tip/kernel/time/Kconfig =================================================================== --- tip.orig/kernel/time/Kconfig +++ tip/kernel/time/Kconfig @@ -12,6 +12,11 @@ config CLOCKSOURCE_WATCHDOG config ARCH_CLOCKSOURCE_DATA bool +# Clocksources require validation of the clocksource against the last +# cycle update - x86/TSC misfeature +config CLOCKSOURCE_VALIDATE_LAST_CYCLE + bool + # Timekeeping vsyscall support config GENERIC_TIME_VSYSCALL bool Index: tip/kernel/time/timekeeping_internal.h =================================================================== --- tip.orig/kernel/time/timekeeping_internal.h +++ tip/kernel/time/timekeeping_internal.h @@ -12,9 +12,18 @@ extern void tk_debug_account_sleep_time( #define tk_debug_account_sleep_time(x) #endif +#ifdef CONFIG_CLOCKSOURCE_VALIDATE_LAST_CYCLE +static inline cycle_t clocksource_delta(cycle_t now, cycle_t last, cycle_t mask) +{ + cycle_t ret = (now - last) & mask; + + return (s64) ret > 0 ? ret : 0; +} +#else static inline cycle_t clocksource_delta(cycle_t now, cycle_t last, cycle_t mask) { return (now - last) & mask; } +#endif #endif /* _TIMEKEEPING_INTERNAL_H */