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=-8.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 EA88DC433DF for ; Mon, 3 Aug 2020 13:27:38 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (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 B4F0220738 for ; Mon, 3 Aug 2020 13:27:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="x6fFXknb" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B4F0220738 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=45CJRwcoWKbsjQQbTnP/D7ga7jJLIYrO3oiHmUHNhAw=; b=x6fFXknb6AhvbNevdrO3lXZ02 GUp8lyaHBoTSMMPrRjFYLcxNJlMyZsp48EZeVWNChk1VHN1bZuiyh+010eegdlLrjMm4QwdrCd8Z7 9oQntHskkf3XlQnWbVEFT2Hms1AgaN4h8EhAiRvLYG/NAymf278ygftW9Yv3LFrwgdeiEPlhptK4a 3mMFH/635SiiwcDofykpL8Rpjr98FohBbphRt7zZAoOsivo9UJmDwR+79axbMQNsmwF3lysJvcbA3 htuspkKr9EpbetkyHaydRCEq85qLtRK5X5Wzz3Lk9ssz+HKHPAGq/Q0nHxhZD52+eDPt5JULwQ7CI xTRdeEvfw==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1k2aTv-0003pJ-PZ; Mon, 03 Aug 2020 13:26:23 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1k2aTt-0003nu-9D for linux-arm-kernel@lists.infradead.org; Mon, 03 Aug 2020 13:26:22 +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 1740230E; Mon, 3 Aug 2020 06:26:19 -0700 (PDT) Received: from localhost (unknown [10.1.198.53]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id AC5A63F71F; Mon, 3 Aug 2020 06:26:18 -0700 (PDT) Date: Mon, 3 Aug 2020 14:26:17 +0100 From: Ionela Voinescu To: Viresh Kumar Subject: Re: [PATCH v2 1/7] cpufreq: move invariance setter calls in cpufreq core Message-ID: <20200803132617.GA9512@arm.com> References: <20200722093732.14297-1-ionela.voinescu@arm.com> <20200722093732.14297-2-ionela.voinescu@arm.com> <20200730034128.k4fmblfuwjcmqdze@vireshk-mac-ubuntu> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200730034128.k4fmblfuwjcmqdze@vireshk-mac-ubuntu> User-Agent: Mutt/1.9.4 (2018-02-28) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200803_092621_436379_22FFC0C0 X-CRM114-Status: GOOD ( 24.33 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Rafael J. Wysocki" , Peter Zijlstra , Catalin Marinas , Linux PM , "Rafael J. Wysocki" , Russell King - ARM Linux , Linux Kernel Mailing List , Valentin Schneider , Ingo Molnar , Sudeep Holla , Will Deacon , Dietmar Eggemann , Linux ARM Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi guys, On Thursday 30 Jul 2020 at 09:11:28 (+0530), Viresh Kumar wrote: > On 27-07-20, 15:48, Rafael J. Wysocki wrote: > > On Wed, Jul 22, 2020 at 11:38 AM Ionela Voinescu > > wrote: > > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c > > > index 036f4cc42ede..bac4101546db 100644 > > > --- a/drivers/cpufreq/cpufreq.c > > > +++ b/drivers/cpufreq/cpufreq.c > > > @@ -2058,9 +2058,16 @@ EXPORT_SYMBOL(cpufreq_unregister_notifier); > > > unsigned int cpufreq_driver_fast_switch(struct cpufreq_policy *policy, > > > unsigned int target_freq) > > > { > > > + unsigned int freq; > > > + > > > target_freq = clamp_val(target_freq, policy->min, policy->max); > > > + freq = cpufreq_driver->fast_switch(policy, target_freq); > > > + > > > + if (freq) > > > + arch_set_freq_scale(policy->related_cpus, freq, > > > + policy->cpuinfo.max_freq); > > > > Why can't arch_set_freq_scale() handle freq == 0? > Sorry, I seem to have missed this question the first time around. arch_set_freq_scale() could handle freq == 0, but given that freq == 0 is signaling an error here, I do believe this check is well placed, to prevent a useless call to arch_set_freq_scale(). Also [1]: """ * If 0 is returned by the driver's ->fast_switch() callback to indicate an * error condition, the hardware configuration must be preserved. */ """ > Actually there is no need to. AFAIU the freq returned by fast_switch > can never be 0 (yeah qcom driver does it right now and I am fixing > it). And so we can drop this check altogether. > It's not only the qcom driver, it's also the scmi driver that could return 0 [2]. But I don't think "fixing" these drivers is the solution, given that 0 is indicated as a valid return value of .fast_switch() to signal an error condition [1], while schedutil (the caller), also does validation that the returned frequency is !0 before setting it as current frequency [3]. Therefore, it is know and (somewhat) documented that 0 indicates an error condition and it should be allowed as a return value for .fast_switch(). Also, I believe is a good idea to leave the option for drivers to return 0 (signaling error) from their implementation of .fast_switch(). [1] https://elixir.bootlin.com/linux/v5.8-rc4/source/drivers/cpufreq/cpufreq.c#L2043 [2] https://elixir.bootlin.com/linux/v5.8-rc4/source/drivers/cpufreq/scmi-cpufreq.c#L76 [3] https://elixir.bootlin.com/linux/v5.8-rc4/source/kernel/sched/cpufreq_schedutil.c#L124 Thanks, Ionela. > -- > viresh _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel