From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754760AbcK2RMQ (ORCPT ); Tue, 29 Nov 2016 12:12:16 -0500 Received: from terminus.zytor.com ([198.137.202.10]:38676 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752526AbcK2RMJ (ORCPT ); Tue, 29 Nov 2016 12:12:09 -0500 Date: Tue, 29 Nov 2016 09:11:55 -0800 From: tip-bot for Joel Fernandes Message-ID: Cc: prarit@redhat.com, tglx@linutronix.de, rostedt@goodmis.org, mingo@kernel.org, linux-kernel@vger.kernel.org, richardcochran@gmail.com, john.stultz@linaro.org, hpa@zytor.com, joelaf@google.com Reply-To: joelaf@google.com, john.stultz@linaro.org, richardcochran@gmail.com, mingo@kernel.org, linux-kernel@vger.kernel.org, hpa@zytor.com, rostedt@goodmis.org, tglx@linutronix.de, prarit@redhat.com In-Reply-To: <1480372524-15181-6-git-send-email-john.stultz@linaro.org> References: <1480372524-15181-6-git-send-email-john.stultz@linaro.org> To: linux-tip-commits@vger.kernel.org Subject: [tip:timers/core] timekeeping: Add a fast and NMI safe boot clock Git-Commit-ID: 948a5312f41658f7b76a598a139ef1f4dea09ca9 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: 948a5312f41658f7b76a598a139ef1f4dea09ca9 Gitweb: http://git.kernel.org/tip/948a5312f41658f7b76a598a139ef1f4dea09ca9 Author: Joel Fernandes AuthorDate: Mon, 28 Nov 2016 14:35:22 -0800 Committer: Thomas Gleixner CommitDate: Tue, 29 Nov 2016 18:02:59 +0100 timekeeping: Add a fast and NMI safe boot clock This boot clock can be used as a tracing clock and will account for suspend time. To keep it NMI safe since we're accessing from tracing, we're not using a separate timekeeper with updates to monotonic clock and boot offset protected with seqlocks. This has the following minor side effects: (1) Its possible that a timestamp be taken after the boot offset is updated but before the timekeeper is updated. If this happens, the new boot offset is added to the old timekeeping making the clock appear to update slightly earlier: CPU 0 CPU 1 timekeeping_inject_sleeptime64() __timekeeping_inject_sleeptime(tk, delta); timestamp(); timekeeping_update(tk, TK_CLEAR_NTP...); (2) On 32-bit systems, the 64-bit boot offset (tk->offs_boot) may be partially updated. Since the tk->offs_boot update is a rare event, this should be a rare occurrence which postprocessing should be able to handle. Signed-off-by: Joel Fernandes Signed-off-by: John Stultz Reviewed-by: Thomas Gleixner Cc: Prarit Bhargava Cc: Richard Cochran Cc: Steven Rostedt Link: http://lkml.kernel.org/r/1480372524-15181-6-git-send-email-john.stultz@linaro.org Signed-off-by: Thomas Gleixner --- include/linux/timekeeping.h | 1 + kernel/time/timekeeping.c | 29 +++++++++++++++++++++++++++++ 2 files changed, 30 insertions(+) diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h index 09168c5..361f8bf 100644 --- a/include/linux/timekeeping.h +++ b/include/linux/timekeeping.h @@ -249,6 +249,7 @@ static inline u64 ktime_get_raw_ns(void) extern u64 ktime_get_mono_fast_ns(void); extern u64 ktime_get_raw_fast_ns(void); +extern u64 ktime_get_boot_fast_ns(void); /* * Timespec interfaces utilizing the ktime based ones diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 37dec7e..b2286e9 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -425,6 +425,35 @@ u64 ktime_get_raw_fast_ns(void) } EXPORT_SYMBOL_GPL(ktime_get_raw_fast_ns); +/** + * ktime_get_boot_fast_ns - NMI safe and fast access to boot clock. + * + * To keep it NMI safe since we're accessing from tracing, we're not using a + * separate timekeeper with updates to monotonic clock and boot offset + * protected with seqlocks. This has the following minor side effects: + * + * (1) Its possible that a timestamp be taken after the boot offset is updated + * but before the timekeeper is updated. If this happens, the new boot offset + * is added to the old timekeeping making the clock appear to update slightly + * earlier: + * CPU 0 CPU 1 + * timekeeping_inject_sleeptime64() + * __timekeeping_inject_sleeptime(tk, delta); + * timestamp(); + * timekeeping_update(tk, TK_CLEAR_NTP...); + * + * (2) On 32-bit systems, the 64-bit boot offset (tk->offs_boot) may be + * partially updated. Since the tk->offs_boot update is a rare event, this + * should be a rare occurrence which postprocessing should be able to handle. + */ +u64 notrace ktime_get_boot_fast_ns(void) +{ + struct timekeeper *tk = &tk_core.timekeeper; + + return (ktime_get_mono_fast_ns() + ktime_to_ns(tk->offs_boot)); +} +EXPORT_SYMBOL_GPL(ktime_get_boot_fast_ns); + /* Suspend-time cycles value for halted fast timekeeper. */ static cycle_t cycles_at_suspend;