From nobody Mon May 11 04:52:13 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id EC982C433F5 for ; Thu, 14 Apr 2022 09:18:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241636AbiDNJUu (ORCPT ); Thu, 14 Apr 2022 05:20:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40848 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241167AbiDNJUi (ORCPT ); Thu, 14 Apr 2022 05:20:38 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3483E5130A; Thu, 14 Apr 2022 02:18:14 -0700 (PDT) From: Kurt Kanzenbach DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1649927892; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=a//Ayf6Cd8/CsHAT40buAmbBeRMSfyUjelkzghG9ajI=; b=lPl+ddht5blVzHrAnBdE9KsqTJEZMbBs0aOx2oy1+AV63uIVl5VCDZGsaUbQUgh5+602Xh YTLzkz+i7NNfx7nXFZCglWU8lNN3NDultV74pP+5pecZlhtvV+EiKvrfuZ2fDrrPHi0gV5 0sjY72QxhIReM/h561J/9Mau/6QWDNFcQRhBij6NMmS962JPLyp2sByPQvDC256N7/I0vb mQ7dR5oWOqGl4RUTVmCuStRdmlaVP+syP0VtT6bP828RCyersvUWEkdfP8FSq9I+TXIA3e 5goKc1e6Vde7XzInYq7EIy0uUbzlrsmAOR8s/rk9x4ZNAuxrMkt/7Ze8o81yHg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1649927892; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=a//Ayf6Cd8/CsHAT40buAmbBeRMSfyUjelkzghG9ajI=; b=CZ70hXWPP5URIE/vjVomUR7Egh4Nlo9mlKYwmbtQlb1yGW1SflMkNwffgoxYuBmo0hfQcQ t0JUfnZoDEHbsgDA== To: John Stultz , Thomas Gleixner , Stephen Boyd , Steven Rostedt , Ingo Molnar , Jonathan Corbet Cc: Richard Cochran , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Kurt Kanzenbach Subject: [PATCH v2 1/3] timekeeping: Introduce fast accessor to clock tai Date: Thu, 14 Apr 2022 11:18:03 +0200 Message-Id: <20220414091805.89667-2-kurt@linutronix.de> In-Reply-To: <20220414091805.89667-1-kurt@linutronix.de> References: <20220414091805.89667-1-kurt@linutronix.de> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Introduce fast/NMI safe accessor to clock tai for tracing. The Linux kernel tracing infrastructure has support for using different clocks to generate timestamps for trace events. Especially in TSN networks it's useful to have= TAI as trace clock, because the application scheduling is done in accordance to= the network time, which is based on TAI. With a tai trace_clock in place, it be= comes very convenient to correlate network activity with Linux kernel application traces. Use the same implementation as ktime_get_boot_fast_ns() does by reading the monotonic time and adding the TAI offset. The same limitations as for the f= ast boot implementation apply. The TAI offset may change at run time e.g., by setting the time or using adjtimex() with an offset. However, these kind of offset changes are rare events. Nevertheless, the user has to be aware and = deal with it in post processing. An alternative approach would be to use the same implementation as ktime_get_real_fast_ns() does. However, this requires to add an additional = u64 member to the tk_read_base struct. This struct together with a seqcount is designed to fit into a single cache line on 64 bit architectures. Adding a = new member would violate this constraint. Signed-off-by: Kurt Kanzenbach --- Documentation/core-api/timekeeping.rst | 1 + include/linux/timekeeping.h | 1 + kernel/time/timekeeping.c | 17 +++++++++++++++++ 3 files changed, 19 insertions(+) diff --git a/Documentation/core-api/timekeeping.rst b/Documentation/core-ap= i/timekeeping.rst index 729e24864fe7..22ec68f24421 100644 --- a/Documentation/core-api/timekeeping.rst +++ b/Documentation/core-api/timekeeping.rst @@ -132,6 +132,7 @@ Some additional variants exist for more specialized cas= es: .. c:function:: u64 ktime_get_mono_fast_ns( void ) u64 ktime_get_raw_fast_ns( void ) u64 ktime_get_boot_fast_ns( void ) + u64 ktime_get_tai_fast_ns( void ) u64 ktime_get_real_fast_ns( void ) =20 These variants are safe to call from any context, including from diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h index 78a98bdff76d..fe1e467ba046 100644 --- a/include/linux/timekeeping.h +++ b/include/linux/timekeeping.h @@ -177,6 +177,7 @@ 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); +extern u64 ktime_get_tai_fast_ns(void); extern u64 ktime_get_real_fast_ns(void); =20 /* diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index dcdcb85121e4..2c22023fbf5f 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -532,6 +532,23 @@ u64 notrace ktime_get_boot_fast_ns(void) } EXPORT_SYMBOL_GPL(ktime_get_boot_fast_ns); =20 +/** + * ktime_get_tai_fast_ns - NMI safe and fast access to tai clock. + * + * The same limitations as described for ktime_get_boot_fast_ns() apply. T= he + * mono time and the TAI offset are not read atomically which may yield wr= ong + * readouts. However, an update of the TAI offset is an rare event e.g., c= aused + * by settime or adjtimex with an offset. The user of this function has to= deal + * with the possibility of wrong timestamps in post processing. + */ +u64 notrace ktime_get_tai_fast_ns(void) +{ + struct timekeeper *tk =3D &tk_core.timekeeper; + + return (ktime_get_mono_fast_ns() + ktime_to_ns(data_race(tk->offs_tai))); +} +EXPORT_SYMBOL_GPL(ktime_get_tai_fast_ns); + static __always_inline u64 __ktime_get_real_fast(struct tk_fast *tkf, u64 = *mono) { struct tk_read_base *tkr; --=20 2.30.2 From nobody Mon May 11 04:52:13 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7394BC433EF for ; Thu, 14 Apr 2022 09:18:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241618AbiDNJUo (ORCPT ); Thu, 14 Apr 2022 05:20:44 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40846 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241162AbiDNJUi (ORCPT ); Thu, 14 Apr 2022 05:20:38 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 786EB51312; Thu, 14 Apr 2022 02:18:14 -0700 (PDT) From: Kurt Kanzenbach DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1649927893; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=YlxWxeEGkgLnVt3u2pgdSqjRibYcLflLeZsegRG9WOc=; b=woA4MM1nalDUbF5qByr5OrBaLP7a5QmD3vxg+EGDy9AV7h0kQexg01M+J801NGmDK5Yg36 MegPwzTgDfDGGTOSwH4FYz/HTngLe1bYBBO697YTTfEiy4tTLaikGgtBSrWDfepkhDZ5qQ dMOdbfNCzg7um5DRLP977CmoerlO0gR7QZ/YuG0c9izsqwa/5ssRuARbilkvgCgYRm08Hw b1AftCe7fPuNs0c88r+9q9+reHruSAIWA7V1eg6X4szqXL1BSe7QeoDUMqkSASEzYBSMKQ FoelKpto4IcKmr0h0oZwHBFh3NSTy2C5361MWnJVgcXiCXJwINjIGR+SomoHxw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1649927893; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=YlxWxeEGkgLnVt3u2pgdSqjRibYcLflLeZsegRG9WOc=; b=TrVTrdBxZf6P1A7fu27oe3ucmEXu0kBss2Q6deigtyXa+CA3Kjl7ePQI1NoxVkBLowQnN/ 2nyJAW2UpLWqdHDw== To: John Stultz , Thomas Gleixner , Stephen Boyd , Steven Rostedt , Ingo Molnar , Jonathan Corbet Cc: Richard Cochran , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Kurt Kanzenbach Subject: [PATCH v2 2/3] tracing: Introduce trace clock tai Date: Thu, 14 Apr 2022 11:18:04 +0200 Message-Id: <20220414091805.89667-3-kurt@linutronix.de> In-Reply-To: <20220414091805.89667-1-kurt@linutronix.de> References: <20220414091805.89667-1-kurt@linutronix.de> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" A fast/NMI safe accessor for CLOCK_TAI has been introduced. Use it for adding the additional trace clock "tai". Signed-off-by: Kurt Kanzenbach --- kernel/trace/trace.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index f4de111fa18f..7be87b29c6c1 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -1542,6 +1542,7 @@ static struct { { ktime_get_mono_fast_ns, "mono", 1 }, { ktime_get_raw_fast_ns, "mono_raw", 1 }, { ktime_get_boot_fast_ns, "boot", 1 }, + { ktime_get_tai_fast_ns, "tai", 1 }, ARCH_TRACE_CLOCKS }; =20 --=20 2.30.2 From nobody Mon May 11 04:52:13 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0AEE1C433EF for ; Thu, 14 Apr 2022 09:18:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241646AbiDNJUz (ORCPT ); Thu, 14 Apr 2022 05:20:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40858 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241602AbiDNJUj (ORCPT ); Thu, 14 Apr 2022 05:20:39 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 10E1251E4D; Thu, 14 Apr 2022 02:18:15 -0700 (PDT) From: Kurt Kanzenbach DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1649927893; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=iLmCDPlHlx+4vJ7+eT/pCoYu1/+sbjT/6wC8EGaZi10=; b=Ouz9SoFspDW418thOwaQ0Wmr2WP5cb7znTdJES07Jqk9ljP7qEuX4Ja0bp2p9Bx1rL46+0 KEM/ThW4kR7QqxstcwNG1UBJMbrSEcivkYgDo2AA3pJHs6Vv+FzGnev/fhr1PZlTqUDAWd 6f2Z2ddOjcAn5KCI+LKeV41G5Wyutpu08s+KxiTMHy/EPTRQLGrsB+Xt4YKuI6fXJkLvno 4K89hh3dbaTp+7PlMhnUVQK4fYa+WiGDSzXbiAzGiLOtHyRA3iNtaSgJD9QlQ+dOltQ2nK RblARhI6wi4jP2x1Os0ZUdTxZUAMvhPMUzyZMgTeX2JXgl3mXcUdKIDh8hJV+g== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1649927893; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=iLmCDPlHlx+4vJ7+eT/pCoYu1/+sbjT/6wC8EGaZi10=; b=Fup1SrnNBv5FuCo7x/lZ5UGJZXakS/VRTQw77bfksXFJPu8+Pso4qvtggfACDwPEjBiz36 3b1SHOh6BLCvwJAA== To: John Stultz , Thomas Gleixner , Stephen Boyd , Steven Rostedt , Ingo Molnar , Jonathan Corbet Cc: Richard Cochran , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Kurt Kanzenbach Subject: [PATCH v2 3/3] tracing: Add documentation for trace clock tai Date: Thu, 14 Apr 2022 11:18:05 +0200 Message-Id: <20220414091805.89667-4-kurt@linutronix.de> In-Reply-To: <20220414091805.89667-1-kurt@linutronix.de> References: <20220414091805.89667-1-kurt@linutronix.de> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Add documentation for newly introduced trace clock "tai". This clock corresponds to CLOCK_TAI. Signed-off-by: Kurt Kanzenbach --- Documentation/trace/ftrace.rst | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst index 45b8c56af67a..b37dc19e4d40 100644 --- a/Documentation/trace/ftrace.rst +++ b/Documentation/trace/ftrace.rst @@ -517,6 +517,18 @@ of ftrace. Here is a list of some of the key files: processing should be able to handle them. See comments in the ktime_get_boot_fast_ns() function for more information. =20 + tai: + This is the tai clock (CLOCK_TAI) and is derived from the wall- + clock time. However, this clock does not experience + discontinuities and backwards jumps caused by NTP inserting leap + seconds. Since the clock access is designed for use in tracing, + side effects are possible. The clock access may yield wrong + readouts in case the internal TAI offset is updated e.g., caused + by setting the system time or using adjtimex() with an offset. + These effects are rare and post processing should be able to + handle them. See comments in the ktime_get_tai_fast_ns() + function for more information. + To set a clock, simply echo the clock name into this file:: =20 # echo global > trace_clock --=20 2.30.2