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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 B34DDC43219 for ; Tue, 30 Apr 2019 15:27:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 71AFD21707 for ; Tue, 30 Apr 2019 15:27:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726090AbfD3P1t (ORCPT ); Tue, 30 Apr 2019 11:27:49 -0400 Received: from foss.arm.com ([217.140.101.70]:49180 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725942AbfD3P1t (ORCPT ); Tue, 30 Apr 2019 11:27:49 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id E0BE6374; Tue, 30 Apr 2019 08:27:48 -0700 (PDT) Received: from [10.1.196.92] (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id ECEC73F719; Tue, 30 Apr 2019 08:27:46 -0700 (PDT) Subject: Re: [PATCH 7/7] clocksource/arm_arch_timer: Use arch_timer_read_counter to access stable counters To: Daniel Lezcano , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Cc: Russell King , Will Deacon , Catalin Marinas , Mark Rutland , Wim Van Sebroeck , Guenter Roeck , Valentin Schneider References: <20190408154907.223536-1-marc.zyngier@arm.com> <20190408154907.223536-8-marc.zyngier@arm.com> <2a60a031-1eab-2d5e-89ff-b5d516545eeb@linaro.org> 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 ZXIgPG1hcmMuenluZ2llckBhcm0uY29tPokCOwQTAQIAJQIbAwYLCQgHAwIGFQgCCQoLBBYC AwECHgECF4AFAk6NvYYCGQEACgkQI9DQutE9ekObww/+NcUATWXOcnoPflpYG43GZ0XjQLng LQFjBZL+CJV5+1XMDfz4ATH37cR+8gMO1UwmWPv5tOMKLHhw6uLxGG4upPAm0qxjRA/SE3LC 22kBjWiSMrkQgv5FDcwdhAcj8A+gKgcXBeyXsGBXLjo5UQOGvPTQXcqNXB9A3ZZN9vS6QUYN TXFjnUnzCJd+PVI/4jORz9EUVw1q/+kZgmA8/GhfPH3xNetTGLyJCJcQ86acom2liLZZX4+1 6Hda2x3hxpoQo7pTu+XA2YC4XyUstNDYIsE4F4NVHGi88a3N8yWE+Z7cBI2HjGvpfNxZnmKX 6bws6RQ4LHDPhy0yzWFowJXGTqM/e79c1UeqOVxKGFF3VhJJu1nMlh+5hnW4glXOoy/WmDEM UMbl9KbJUfo+GgIQGMp8mwgW0vK4HrSmevlDeMcrLdfbbFbcZLNeFFBn6KqxFZaTd+LpylIH bOPN6fy1Dxf7UZscogYw5Pt0JscgpciuO3DAZo3eXz6ffj2NrWchnbj+SpPBiH4srfFmHY+Y LBemIIOmSqIsjoSRjNEZeEObkshDVG5NncJzbAQY+V3Q3yo9og/8ZiaulVWDbcpKyUpzt7pv cdnY3baDE8ate/cymFP5jGJK++QCeA6u6JzBp7HnKbngqWa6g8qDSjPXBPCLmmRWbc5j0lvA 6ilrF8m5Ag0ETol/RQEQAM/2pdLYCWmf3rtIiP8Wj5NwyjSL6/UrChXtoX9wlY8a4h3EX6E3 64snIJVMLbyr4bwdmPKULlny7T/R8dx/mCOWu/DztrVNQiXWOTKJnd/2iQblBT+W5W8ep/nS w3qUIckKwKdplQtzSKeE+PJ+GMS+DoNDDkcrVjUnsoCEr0aK3cO6g5hLGu8IBbC1CJYSpple VVb/sADnWF3SfUvJ/l4K8Uk4B4+X90KpA7U9MhvDTCy5mJGaTsFqDLpnqp/yqaT2P7kyMG2E w+eqtVIqwwweZA0S+tuqput5xdNAcsj2PugVx9tlw/LJo39nh8NrMxAhv5aQ+JJ2I8UTiHLX QvoC0Yc/jZX/JRB5r4x4IhK34Mv5TiH/gFfZbwxd287Y1jOaD9lhnke1SX5MXF7eCT3cgyB+ hgSu42w+2xYl3+rzIhQqxXhaP232t/b3ilJO00ZZ19d4KICGcakeiL6ZBtD8TrtkRiewI3v0 o8rUBWtjcDRgg3tWx/PcJvZnw1twbmRdaNvsvnlapD2Y9Js3woRLIjSAGOijwzFXSJyC2HU1 AAuR9uo4/QkeIrQVHIxP7TJZdJ9sGEWdeGPzzPlKLHwIX2HzfbdtPejPSXm5LJ026qdtJHgz BAb3NygZG6BH6EC1NPDQ6O53EXorXS1tsSAgp5ZDSFEBklpRVT3E0NrDABEBAAGJAh8EGAEC AAkFAk6Jf0UCGwwACgkQI9DQutE9ekMLBQ//U+Mt9DtFpzMCIHFPE9nNlsCm75j22lNiw6mX mx3cUA3pl+uRGQr/zQC5inQNtjFUmwGkHqrAw+SmG5gsgnM4pSdYvraWaCWOZCQCx1lpaCOl MotrNcwMJTJLQGc4BjJyOeSH59HQDitKfKMu/yjRhzT8CXhys6R0kYMrEN0tbe1cFOJkxSbV 0GgRTDF4PKyLT+RncoKxQe8lGxuk5614aRpBQa0LPafkirwqkUtxsPnarkPUEfkBlnIhAR8L kmneYLu0AvbWjfJCUH7qfpyS/FRrQCoBq9QIEcf2v1f0AIpA27f9KCEv5MZSHXGCdNcbjKw1 39YxYZhmXaHFKDSZIC29YhQJeXWlfDEDq6nIhvurZy3mSh2OMQgaIoFexPCsBBOclH8QUtMk a3jW/qYyrV+qUq9Wf3SKPrXf7B3xB332jFCETbyZQXqmowV+2b3rJFRWn5hK5B+xwvuxKyGq qDOGjof2dKl2zBIxbFgOclV7wqCVkhxSJi/QaOj2zBqSNPXga5DWtX3ekRnJLa1+ijXxmdjz hApihi08gwvP5G9fNGKQyRETePEtEAWt0b7dOqMzYBYGRVr7uS4uT6WP7fzOwAJC4lU7ZYWZ yVshCa0IvTtp1085RtT3qhh9mobkcZ+7cQOY+Tx2RGXS9WeOh2jZjdoWUv6CevXNQyOUXMM= Organization: ARM Ltd Message-ID: Date: Tue, 30 Apr 2019 16:27:43 +0100 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <2a60a031-1eab-2d5e-89ff-b5d516545eeb@linaro.org> 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 15/04/2019 13:16, Daniel Lezcano wrote: > On 08/04/2019 17:49, Marc Zyngier wrote: >> Instead of always going via arch_counter_get_cntvct_stable to >> access the counter workaround, let's have arch_timer_read_counter >> to point to the right method. >> >> For that, we need to track whether any CPU in the system has a >> workaround for the counter. This is done by having an atomic >> variable tracking this. >> >> Signed-off-by: Marc Zyngier >> --- > > [ ... ] > >> + >> /* >> * Default to cp15 based access because arm64 uses this function for >> * sched_clock() before DT is probed and the cp15 method is guaranteed >> @@ -372,6 +392,7 @@ static u32 notrace sun50i_a64_read_cntv_tval_el0(void) >> DEFINE_PER_CPU(const struct arch_timer_erratum_workaround *, timer_unstable_counter_workaround); >> EXPORT_SYMBOL_GPL(timer_unstable_counter_workaround); >> >> +static atomic_t timer_unstable_counter_workaround_in_use = ATOMIC_INIT(0); > > Wouldn't make sense to READ_ONCE / WRITE_ONCE instead of using an atomic? I don't think *_ONCE says anything about the atomicity of the access. It only instruct the compiler that this should only be accessed once, and not reloaded/rewritten. In this case, WRITE_ONCE() would work just as well, but I feel that setting the expectations do matter. I also had a vague idea to use this as a refcount to drop the workarounds as CPUs get hotplugged off, in which case we'd need the RMW operations to be atomic. Anyway, I'm not hell bent on this. If you fundamentally disagree with me I'll change it. Thanks, M. -- Jazz is not dead. It just smells funny... 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=-4.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS 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 D09D1C43219 for ; Tue, 30 Apr 2019 15:27:59 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 9E30A2147A for ; Tue, 30 Apr 2019 15:27:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="bI0ChqUV" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9E30A2147A Authentication-Results: mail.kernel.org; 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Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <2a60a031-1eab-2d5e-89ff-b5d516545eeb@linaro.org> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190430_082751_674460_D759F0EA X-CRM114-Status: GOOD ( 17.77 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Russell King , Catalin Marinas , Will Deacon , Wim Van Sebroeck , Valentin Schneider , Guenter Roeck Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 15/04/2019 13:16, Daniel Lezcano wrote: > On 08/04/2019 17:49, Marc Zyngier wrote: >> Instead of always going via arch_counter_get_cntvct_stable to >> access the counter workaround, let's have arch_timer_read_counter >> to point to the right method. >> >> For that, we need to track whether any CPU in the system has a >> workaround for the counter. This is done by having an atomic >> variable tracking this. >> >> Signed-off-by: Marc Zyngier >> --- > > [ ... ] > >> + >> /* >> * Default to cp15 based access because arm64 uses this function for >> * sched_clock() before DT is probed and the cp15 method is guaranteed >> @@ -372,6 +392,7 @@ static u32 notrace sun50i_a64_read_cntv_tval_el0(void) >> DEFINE_PER_CPU(const struct arch_timer_erratum_workaround *, timer_unstable_counter_workaround); >> EXPORT_SYMBOL_GPL(timer_unstable_counter_workaround); >> >> +static atomic_t timer_unstable_counter_workaround_in_use = ATOMIC_INIT(0); > > Wouldn't make sense to READ_ONCE / WRITE_ONCE instead of using an atomic? I don't think *_ONCE says anything about the atomicity of the access. It only instruct the compiler that this should only be accessed once, and not reloaded/rewritten. In this case, WRITE_ONCE() would work just as well, but I feel that setting the expectations do matter. I also had a vague idea to use this as a refcount to drop the workarounds as CPUs get hotplugged off, in which case we'd need the RMW operations to be atomic. Anyway, I'm not hell bent on this. If you fundamentally disagree with me I'll change it. Thanks, M. -- Jazz is not dead. It just smells funny... _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel