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=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, 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 3BE5DC2BA83 for ; Wed, 12 Feb 2020 09:30:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0DDCD20873 for ; Wed, 12 Feb 2020 09:30:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728773AbgBLJaj (ORCPT ); Wed, 12 Feb 2020 04:30:39 -0500 Received: from foss.arm.com ([217.140.110.172]:57938 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728530AbgBLJaj (ORCPT ); Wed, 12 Feb 2020 04:30:39 -0500 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 D521130E; Wed, 12 Feb 2020 01:30:38 -0800 (PST) Received: from [10.1.194.46] (e113632-lin.cambridge.arm.com [10.1.194.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D400A3F6CF; Wed, 12 Feb 2020 01:30:36 -0800 (PST) Subject: Re: [PATCH v3 7/7] clocksource/drivers/arm_arch_timer: validate arch_timer_rate To: Ionela Voinescu , catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com, maz@kernel.org, suzuki.poulose@arm.com, sudeep.holla@arm.com, lukasz.luba@arm.com, rjw@rjwysocki.net Cc: peterz@infradead.org, mingo@redhat.com, vincent.guittot@linaro.org, viresh.kumar@linaro.org, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org References: <20200211184542.29585-1-ionela.voinescu@arm.com> <20200211184542.29585-8-ionela.voinescu@arm.com> From: Valentin Schneider Message-ID: <05e257b6-0a39-135d-8117-7883739538c3@arm.com> Date: Wed, 12 Feb 2020 09:30:34 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20200211184542.29585-8-ionela.voinescu@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On 11/02/2020 18:45, Ionela Voinescu wrote: > From: Valentin Schneider > > Using an arch timer with a frequency of less than 1MHz can result in an > incorrect functionality of the system which assumes a reasonable rate. > > One example is the use of activity monitors for frequency invariance > which uses the rate of the arch timer as the known rate of the constant > cycle counter in computing its ratio compared to the maximum frequency > of a CPU. For arch timer frequencies less than 1MHz this ratio could > end up being 0 which is an invalid value for its use. > I'm being pedantic here (as usual), but I'd contrast this a bit more. The activity monitor code checks by itself that the ratio doesn't end up being 0, which is why we don't slam the brakes if the arch timer freq is < 1MHz. It's just a CNTFRQ sanity check that goes a bit beyond the 0 value check, IMO. > Therefore, warn if the arch timer rate is below 1MHz which contravenes > the recommended architecture interval of 1 to 50MHz. > > Signed-off-by: Ionela Voinescu > Cc: Mark Rutland > Cc: Marc Zyngier ISTR something somewhere that says the first signoff should be that of the author of the patch, and seeing as I just provided an untested diff that ought to be you :)