From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C77D7C76188 for ; Mon, 22 Jul 2019 12:48:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A30E7218D4 for ; Mon, 22 Jul 2019 12:48:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729728AbfGVMsG (ORCPT ); Mon, 22 Jul 2019 08:48:06 -0400 Received: from foss.arm.com ([217.140.110.172]:36918 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729085AbfGVMsG (ORCPT ); Mon, 22 Jul 2019 08:48:06 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 09B87344; Mon, 22 Jul 2019 05:48:05 -0700 (PDT) Received: from [10.1.197.61] (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E7EAE3F71A; Mon, 22 Jul 2019 05:48:02 -0700 (PDT) Subject: Re: [PATCH 1/3] printk: Allow architecture-specific timestamping function To: Petr Mladek Cc: Catalin Marinas , Mark Rutland , Will Deacon , Sergey Senozhatsky , Steven Rostedt , John Stultz , Thomas Gleixner , Pavel Tatashin , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20190722103330.255312-1-marc.zyngier@arm.com> <20190722103330.255312-2-marc.zyngier@arm.com> <20190722112543.5quvqgerpyvfgbxq@pathway.suse.cz> From: Marc Zyngier Openpgp: preference=signencrypt Autocrypt: addr=marc.zyngier@arm.com; prefer-encrypt=mutual; keydata= mQINBE6Jf0UBEADLCxpix34Ch3kQKA9SNlVQroj9aHAEzzl0+V8jrvT9a9GkK+FjBOIQz4KE g+3p+lqgJH4NfwPm9H5I5e3wa+Scz9wAqWLTT772Rqb6hf6kx0kKd0P2jGv79qXSmwru28vJ t9NNsmIhEYwS5eTfCbsZZDCnR31J6qxozsDHpCGLHlYym/VbC199Uq/pN5gH+5JHZyhyZiNW ozUCjMqC4eNW42nYVKZQfbj/k4W9xFfudFaFEhAf/Vb1r6F05eBP1uopuzNkAN7vqS8XcgQH qXI357YC4ToCbmqLue4HK9+2mtf7MTdHZYGZ939OfTlOGuxFW+bhtPQzsHiW7eNe0ew0+LaL 3wdNzT5abPBscqXWVGsZWCAzBmrZato+Pd2bSCDPLInZV0j+rjt7MWiSxEAEowue3IcZA++7 ifTDIscQdpeKT8hcL+9eHLgoSDH62SlubO/y8bB1hV8JjLW/jQpLnae0oz25h39ij4ijcp8N t5slf5DNRi1NLz5+iaaLg4gaM3ywVK2VEKdBTg+JTg3dfrb3DH7ctTQquyKun9IVY8AsxMc6 lxl4HxrpLX7HgF10685GG5fFla7R1RUnW5svgQhz6YVU33yJjk5lIIrrxKI/wLlhn066mtu1 DoD9TEAjwOmpa6ofV6rHeBPehUwMZEsLqlKfLsl0PpsJwov8TQARAQABtCNNYXJjIFp5bmdp ZXIgPG1hcmMuenluZ2llckBhcm0uY29tPokCTwQTAQIAOQIbAwYLCQgHAwIGFQgCCQoLBBYC AwECHgECF4AWIQSf1RxT4LVjGP2VnD0j0NC60T16QwUCXR3BUgAKCRAj0NC60T16Qyd/D/9s x0puxd3lI+jdLMEY8sTsNxw/+CZfyKaHtysasZlloLK7ftYhRUc63mMW2mrvgB1GEnXYIdj3 g6Qo4csoDuN+9EBmejh7SglM/h0evOtrY2V5QmZA/e/Pqfj0P3N/Eb5BiB3R4ptLtvKCTsqr 3womxCRqQY3IrMn1s2qfpmeNLUIfCUtgh8opzPtFuFJWVBzbzvhPEApZzMe9Vs1O2P8BQaay QXpbzHaKruthoLICRzS/3UCe0N/mBZQRKHrqhPwvjZdO0KMqjSsPqfukOJ8bl5jZxYk+G/3T 66Z4JUpZ7RkcrX7CvBfZqRo19WyWFfjGz79iVMJNIEkJvJBANbTSiWUC6IkP+zT/zWYzZPXx XRlrKWSBBqJrWQKZBwKOLsL62oQG7ARvpCG9rZ6hd5CLQtPI9dasgTwOIA1OW2mWzi20jDjD cGC9ifJiyWL8L/bgwyL3F/G0R1gxAfnRUknyzqfpLy5cSgwKCYrXOrRqgHoB+12HA/XQUG+k vKW8bbdVk5XZPc5ghdFIlza/pb1946SrIg1AsjaEMZqunh0G7oQhOWHKOd6fH0qg8NssMqQl jLfFiOlgEV2mnaz6XXQe/viXPwa4NCmdXqxeBDpJmrNMtbEbq+QUbgcwwle4Xx2/07ICkyZH +7RvbmZ/dM9cpzMAU53sLxSIVQT5lj23WLkCDQROiX9FARAAz/al0tgJaZ/eu0iI/xaPk3DK NIvr9SsKFe2hf3CVjxriHcRfoTfriycglUwtvKvhvB2Y8pQuWfLtP9Hx3H+YI5a78PO2tU1C JdY5Momd3/aJBuUFP5blbx6n+dLDepQhyQrAp2mVC3NIp4T48n4YxL4Og0MORytWNSeygISv Rordw7qDmEsa7wgFsLUIlhKmmV5VVv+wAOdYXdJ9S8n+XgrxSTgHj5f3QqkDtT0yG8NMLLmY kZpOwWoMumeqn/KppPY/uTIwbYTD56q1UirDDB5kDRL626qm63nF00ByyPY+6BXH22XD8smj f2eHw2szECG/lpD4knYjxROIctdC+gLRhz+Nlf8lEHmvjHgiErfgy/lOIf+AV9lvDF3bztjW M5oP2WGeR7VJfkxcXt4JPdyDIH6GBK7jbD7bFiXf6vMiFCrFeFo/bfa39veKUk7TRlnX13go gIZxqR6IvpkG0PxOu2RGJ7Aje/SjytQFa2NwNGCDe1bH89wm9mfDW3BuZF1o2+y+eVqkPZj0 mzfChEsiNIAY6KPDMVdInILYdTUAC5H26jj9CR4itBUcjE/tMll0n2wYRZ14Y/PM+UosfAhf YfN9t2096M9JebksnTbqp20keDMEBvc3KBkboEfoQLU08NDo7ncReitdLW2xICCnlkNIUQGS WlFVPcTQ2sMAEQEAAYkCHwQYAQIACQUCTol/RQIbDAAKCRAj0NC60T16QwsFD/9T4y30O0Wn MwIgcU8T2c2WwKbvmPbaU2LDqZebHdxQDemX65EZCv/NALmKdA22MVSbAaQeqsDD5KYbmCyC czilJ1i+tpZoJY5kJALHWWloI6Uyi2s1zAwlMktAZzgGMnI55Ifn0dAOK0p8oy7/KNGHNPwJ eHKzpHSRgysQ3S1t7VwU4mTFJtXQaBFMMXg8rItP5GdygrFB7yUbG6TnrXhpGkFBrQs9p+SK vCqRS3Gw+dquQ9QR+QGWciEBHwuSad5gu7QC9taN8kJQfup+nJL8VGtAKgGr1AgRx/a/V/QA ikDbt/0oIS/kxlIdcYJ01xuMrDXf1jFhmGZdocUoNJkgLb1iFAl5daV8MQOrqciG+6tnLeZK HY4xCBoigV7E8KwEE5yUfxBS0yRreNb+pjKtX6pSr1Z/dIo+td/sHfEHffaMUIRNvJlBeqaj BX7ZveskVFafmErkH7HC+7ErIaqoM4aOh/Z0qXbMEjFsWA5yVXvCoJWSHFImL9Bo6PbMGpI0 9eBrkNa1fd6RGcktrX6KNfGZ2POECmKGLTyDC8/kb180YpDJERN48S0QBa3Rvt06ozNgFgZF Wvu5Li5PpY/t/M7AAkLiVTtlhZnJWyEJrQi9O2nXTzlG1PeqGH2ahuRxn7txA5j5PHZEZdL1 Z46HaNmN2hZS/oJ69c1DI5Rcww== Organization: ARM Ltd Message-ID: <493e2c0b-9536-ce6d-b59e-d169693085da@arm.com> Date: Mon, 22 Jul 2019 13:47:57 +0100 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20190722112543.5quvqgerpyvfgbxq@pathway.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 22/07/2019 12:25, Petr Mladek wrote: > On Mon 2019-07-22 11:33:28, Marc Zyngier wrote: >> printk currently relies on local_clock to time-stamp the kernel >> messages. In order to allow the timestamping (and only that) >> to be overridden by architecture-specific code, let's declare >> a new timestamp_clock() function, which gets used by the printk >> code. Architectures willing to make use of this facility will >> have to define CONFIG_ARCH_HAS_TIMESTAMP_CLOCK. >> >> The default is of course to return local_clock(), so that the >> existing behaviour stays unchanged. >> >> Signed-off-by: Marc Zyngier >> --- >> include/linux/sched/clock.h | 13 +++++++++++++ >> kernel/printk/printk.c | 4 ++-- >> 2 files changed, 15 insertions(+), 2 deletions(-) >> >> diff --git a/include/linux/sched/clock.h b/include/linux/sched/clock.h >> index 867d588314e0..3cf4b2a8ce18 100644 >> --- a/include/linux/sched/clock.h >> +++ b/include/linux/sched/clock.h >> @@ -98,4 +98,17 @@ static inline void enable_sched_clock_irqtime(void) {} >> static inline void disable_sched_clock_irqtime(void) {} >> #endif >> >> +#ifdef CONFIG_ARCH_HAS_TIMESTAMP_CLOCK >> +/* Special need architectures can provide their timestamping function */ > > The commit message and the above comment should be more specific > about what are the special needs. > > It must be clear how and why the clock differs from the other > clocks, especially from lock_clock(). Fair enough. How about something along the lines of: "An architecture can override the timestamp clock (which defaults to local_clock) if local_clock is not significant early enough (sched_clock being available too late)." > Also the first mail says that timestamp_clock() might be > unstable. Is this true only during the early boot or all > the time? With the current proposal, the instability period only exists until sched_clock gets initialized, at which point it takes over and the timestamping becomes stable. Note that this is the arm64 implementation, and not something that is currently guaranteed by just selecting CONFIG_ARCH_HAS_TIMESTAMP_CLOCK. > > The timestamp helps to order the events. An unstable clock > might be better than nothing during the boot. But it would > look strange to use it all the time, especially when it was > unrelated to any other clock used by the system. And that's exactly what patch #3 implements. Once local_clock() returns something significant, we use that. Thanks, M. -- Jazz is not dead. It just smells funny...