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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id EF08ACF11CD for ; Thu, 10 Oct 2024 11:10:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=hjnCrloyll/fxxiMep4t26N6X83JyxrGf/mn+6H22Sk=; b=G4nCblXv18/Oc1rWX5FhZrV1Et HtY0wiYrmVSuHNn5mDa5LiV/Gks/suRBEErB6DH/BE2uyzITz+Eavoa3XZMmWR6/j88fsChSzL82x H5sZqBcz5jczg2XKFWDPZ2rzQd18ZRZGxMV5mXEqQOgZLq6HCZn8w9AXIfrHmzQkCyjFyKQUVCWyz 07wlBlSdEJw+pVxv571OAMwFAayG5wsRFCmdU/VFlW8lF5k8fUiwL5Ydl3xUJ/Z+kx/U6uRFL1YYw voQfNHEPO3YT/Y7w4nS0w3i1CQoy2U5cOGHIL+2fzKmgMT+X7fKf8yo8+H414XeybDdxwgs8oL71F 68sJagKg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1syr3k-0000000CV8e-0G6w; Thu, 10 Oct 2024 11:10:20 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1syr2N-0000000CV0Q-3P3r for linux-arm-kernel@lists.infradead.org; Thu, 10 Oct 2024 11:08:57 +0000 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 16EB5497; Thu, 10 Oct 2024 04:09:23 -0700 (PDT) Received: from arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1F8CF3F58B; Thu, 10 Oct 2024 04:08:48 -0700 (PDT) Date: Thu, 10 Oct 2024 13:08:23 +0200 From: Beata Michalska To: Vanshidhar Konda , viresh.kumar@linaro.org Cc: Sumit Gupta , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-pm@vger.kernel.org, ionela.voinescu@arm.com, sudeep.holla@arm.com, will@kernel.org, catalin.marinas@arm.com, rafael@kernel.org, viresh.kumar@linaro.org, yang@os.amperecomputing.com, lihuisong@huawei.com, zhanjie9@hisilicon.com, linux-tegra , Bibek Basu Subject: Re: [PATCH v7 3/4] arm64: Provide an AMU-based version of arch_freq_avg_get_on_cpu Message-ID: References: <20240913132944.1880703-1-beata.michalska@arm.com> <20240913132944.1880703-4-beata.michalska@arm.com> <5y3yz2ct2o42c53dc6rwpse3andstjx74lowt2b3hohj4ogbct@nu2szdnxvxid> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5y3yz2ct2o42c53dc6rwpse3andstjx74lowt2b3hohj4ogbct@nu2szdnxvxid> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20241010_040855_981532_23897CAA X-CRM114-Status: GOOD ( 44.34 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Oct 03, 2024 at 02:54:22PM -0700, Vanshidhar Konda wrote: > On Thu, Oct 03, 2024 at 11:39:54PM GMT, Beata Michalska wrote: > > On Thu, Sep 26, 2024 at 04:21:14PM -0700, Vanshidhar Konda wrote: > > > On Thu, Sep 26, 2024 at 12:34:01PM GMT, Beata Michalska wrote: > > > > On Tue, Sep 17, 2024 at 05:41:09PM +0530, Sumit Gupta wrote: > > > > > Hi Beata, > > > > Hi Sumit, > > > > > > > > > > Thank you for the patches. > > > > Thank you for having a look at those. > > > > > > > > > > On 13/09/24 18:59, Beata Michalska wrote: > > > > > > External email: Use caution opening links or attachments > > > > > > > > > > > > > > > > > > With the Frequency Invariance Engine (FIE) being already wired up with > > > > > > sched tick and making use of relevant (core counter and constant > > > > > > counter) AMU counters, getting the average frequency for a given CPU, > > > > > > can be achieved by utilizing the frequency scale factor which reflects > > > > > > an average CPU frequency for the last tick period length. > > > > > > > > > > > > The solution is partially based on APERF/MPERF implementation of > > > > > > arch_freq_get_on_cpu. > > > > > > > > > > > > Suggested-by: Ionela Voinescu > > > > > > Signed-off-by: Beata Michalska > > > > > > --- > > > > > > arch/arm64/kernel/topology.c | 109 +++++++++++++++++++++++++++++++---- > > > > > > 1 file changed, 99 insertions(+), 10 deletions(-) > > > > > > > > --- snip ---- > > > > > > > > > > > .. > > > > > freq_comput: > > > > > scale = arch_scale_freq_capacity(cpu); > > > > > freq = scale * arch_scale_freq_ref(cpu); > > > > > ---- > > > > > > > > > This boils down to the question what that function, and the information it > > > > provides, represent really. The 'unknown' here simply says the CPU has been idle > > > > for a while and as such the frequency data is a bit stale and it does not > > > > represent the average freq the CPU is actually running at anymore, which is > > > > the intention here really. Or, that the given CPU is a non-housekeeping one. > > > > Either way I believe this is a useful information, instead of providing > > > > stale data with no indication on whether the frequency is really the 'current' > > > > one or not. > > > > > > > > If that is somehow undesirable we can discuss this further, though I'd rather > > > > avoid exposing an interface where the feedback provided is open to > > > > interpretation at all times. > > > > > > Would it make sense to identify that the frequency reporting is unknown due to > > > cpu being idle vs some other issue like being a non-housekeeping CPU? Would > > > returning a value of 0 make it easier for tools to represent that the CPU is > > > currently idle? > > That is an option. > > Another one would be to return an error for those cases. This would make it > > easier to distinguish between valid frequency &/| idle CPU vs tickless CPU > > (EINVAL vs ENOENT) ? > > > > That seems like a good idea but I suspect it would be confusing to the end user. > > If a user runs `cat /sys/devices/system/cpu/cpu2/cpuinfo_avg_freq` they would > get an error in some cases or get a number in some other iterations. > That is a fair point but I am not entirely convinced using '0' instead makes things any more clearer as this is in no way a valid CPU frequency. As long as we document the expected behaviour keeping the interface well defined, both options should be fine I guess. @Viresh: what is your opinion on that one ? --- BR Beata > Thanks, > Vanshidhar > > > --- > > BR > > Beata > > > > > > Thanks, > > > Vanshidhar > > > > > > > > > > > --- > > > > Best Regards > > > > Beata > > > > > Thank you, > > > > > Sumit Gupta > > > > > > > > > > P.S. Will be on afk for next 2 weeks with no access to email. Please expect > > > > > a delay in response. > > > > > > > > > > > + cpu = ref_cpu; > > > > > > + goto retry; > > > > > > + } > > > > > > + /* > > > > > > + * Reversed computation to the one used to determine > > > > > > + * the arch_freq_scale value > > > > > > + * (see amu_scale_freq_tick for details) > > > > > > + */ > > > > > > + scale = arch_scale_freq_capacity(cpu); > > > > > > + freq = scale * arch_scale_freq_ref(cpu); > > > > > > + freq >>= SCHED_CAPACITY_SHIFT; > > > > > > + return freq; > > > > > > +} > > > > > > + > > > > > > > > > > > static void amu_fie_setup(const struct cpumask *cpus) > > > > > > { > > > > > > int cpu; > > > > > > -- > > > > > > 2.25.1 > > > > > >