From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 117F816130C; Tue, 17 Sep 2024 10:36:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726569402; cv=none; b=gEogT8OEQg7uCmLysOISxAJKV6F+CbL7ja9G7yYcVrGiRfSI0iV9/PDonr+RaNdY5r06mSO37/giZU6GmhgCQeBHUhD0OWCvKoxZHYcqGlPrA5lk8W2n7juillJNfuFTL4bolok8N47ikKOo/dlOvzTcS4igFrYF6Dj+7qMQZRI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726569402; c=relaxed/simple; bh=Q9JsLsOTE9HWlKx4NBBWcpXXbT0Y/JlNm+xqL6UVWgY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=JdJj34NukQCt0d/k8Wd6l21epdzzHK1AtKvh3eosZ6GJJEXr/GcEJ4c3xuuDlyZB0FfEe/337jaejPCYEmG3W9PfOP8EMTFsww/KkBnZNsdES28OVFbF+NuTs1W7QAwcXzyaTp65yeavYsHPEP7ru6pya7I2l0mqinnDqpU98Do= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com 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 D82841007; Tue, 17 Sep 2024 03:37:08 -0700 (PDT) Received: from localhost (ionvoi01-desktop.cambridge.arm.com [10.2.80.58]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1A96B3F64C; Tue, 17 Sep 2024 03:36:39 -0700 (PDT) Date: Tue, 17 Sep 2024 11:36:37 +0100 From: Ionela Voinescu To: Jie Zhan Cc: beata.michalska@arm.com, wangxiongfeng2@huawei.com, viresh.kumar@linaro.org, rafael@kernel.org, linux-pm@vger.kernel.org, linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linuxarm@huawei.com, jonathan.cameron@huawei.com, wanghuiqiang@huawei.com, zhenglifeng1@huawei.com, lihuisong@huawei.com, yangyicong@huawei.com, liaochang1@huawei.com, zengheng4@huawei.com Subject: Re: [PATCH v2 1/3] cppc_cpufreq: Return desired perf in ->get() if feedback counters are 0 Message-ID: References: <20240912072231.439332-1-zhanjie9@hisilicon.com> <20240912072231.439332-2-zhanjie9@hisilicon.com> <79353a26-7304-9d6a-9237-cfa8e7794601@hisilicon.com> Precedence: bulk X-Mailing-List: linux-acpi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <79353a26-7304-9d6a-9237-cfa8e7794601@hisilicon.com> Hi, On Friday 13 Sep 2024 at 20:05:50 (+0800), Jie Zhan wrote: > > Hi Ionela, > > On 12/09/2024 17:43, Ionela Voinescu wrote: > > ... > > > > > A possible (slimmer) alternative implementation for you to consider > > (this merges patches 1 & 2): > > > > diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c > > index bafa32dd375d..c16be9651a6f 100644 > > --- a/drivers/cpufreq/cppc_cpufreq.c > > +++ b/drivers/cpufreq/cppc_cpufreq.c > > @@ -118,6 +118,9 @@ static void cppc_scale_freq_workfn(struct kthread_work *work) > > > > perf = cppc_perf_from_fbctrs(cpu_data, &cppc_fi->prev_perf_fb_ctrs, > > &fb_ctrs); > > + if (!perf) > > + perf = cpu_data->perf_ctrls.desired_perf; > > + > > I think it's better to just return here. > If feedback counters are successfully read but unchanged, the following > calculation and update in cppc_scale_freq_workfn() is meaningless because it > won't change anything. Agreed! > > > cppc_fi->prev_perf_fb_ctrs = fb_ctrs; > > > > perf <<= SCHED_CAPACITY_SHIFT; > > @@ -726,7 +729,7 @@ static int cppc_perf_from_fbctrs(struct cppc_cpudata *cpu_data, > > > > /* Check to avoid divide-by zero and invalid delivered_perf */ > > if (!delta_reference || !delta_delivered) > > - return cpu_data->perf_ctrls.desired_perf; > > + return 0; > > This makes sense to me. > Here is probably why Patch 2 looks bulky. > > > > > return (reference_perf * delta_delivered) / delta_reference; > > } > > @@ -736,7 +739,7 @@ static unsigned int cppc_cpufreq_get_rate(unsigned int cpu) > > struct cppc_perf_fb_ctrs fb_ctrs_t0 = {0}, fb_ctrs_t1 = {0}; > > struct cpufreq_policy *policy = cpufreq_cpu_get(cpu); > > struct cppc_cpudata *cpu_data; > > - u64 delivered_perf; > > + u64 delivered_perf = 0; > > int ret; > > > > if (!policy) > > @@ -747,19 +750,22 @@ static unsigned int cppc_cpufreq_get_rate(unsigned int cpu) > > cpufreq_cpu_put(policy); > > > > ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t0); > > - if (ret) > > - return 0; > > - > > - udelay(2); /* 2usec delay between sampling */ > > - > > - ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t1); > > - if (ret) > > - return 0; > > + if (!ret) { > > + udelay(2); /* 2usec delay between sampling */ > > + ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t1); > > + } > > + if (!ret) > > + delivered_perf = cppc_perf_from_fbctrs(cpu_data, &fb_ctrs_t0, > > + &fb_ctrs_t1); > > TBH, 'if (!ret)' style looks very strange to me. > We haven't done so anywhere in cppc_cpufreq, so let's keep consistency and make > it easier for people to read and maintain? I agree it's a bit of a difficult read, that's why I only sent my code as a suggestion. I did like the benefit of not having to have two different calls to cppc_perf_to_khz() and making the code below common for the error and non-error paths. But it's up to you. > > > + if ((ret == -EFAULT) || !delivered_perf) { > > + if (cppc_get_desired_perf(cpu, &delivered_perf)) > > + delivered_perf = cpu_data->perf_ctrls.desired_perf; > > will take this. > > > + } > > > > - delivered_perf = cppc_perf_from_fbctrs(cpu_data, &fb_ctrs_t0, > > - &fb_ctrs_t1); > > + if (delivered_perf) > > + return cppc_perf_to_khz(&cpu_data->perf_caps, delivered_perf); > > > > - return cppc_perf_to_khz(&cpu_data->perf_caps, delivered_perf); > > + return 0; > > } > > > > disclaimer: not fully checked so likely not "production ready" code :) > > > > Hope it helps, > > Ionela. > > > >> > >> static int cppc_cpufreq_set_boost(struct cpufreq_policy *policy, int state) > >> -- > >> 2.33.0 > >> > > > > How about this? merged patch 1 & 2 as well. > > diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c > index bafa32dd375d..411303f2e8cb 100644 > --- a/drivers/cpufreq/cppc_cpufreq.c > +++ b/drivers/cpufreq/cppc_cpufreq.c > @@ -118,6 +118,9 @@ static void cppc_scale_freq_workfn(struct kthread_work *work) > > perf = cppc_perf_from_fbctrs(cpu_data, &cppc_fi->prev_perf_fb_ctrs, > &fb_ctrs); > + if (!perf) > + return; > + > cppc_fi->prev_perf_fb_ctrs = fb_ctrs; > > perf <<= SCHED_CAPACITY_SHIFT; > @@ -726,7 +729,7 @@ static int cppc_perf_from_fbctrs(struct cppc_cpudata *cpu_data, > > /* Check to avoid divide-by zero and invalid delivered_perf */ > if (!delta_reference || !delta_delivered) > - return cpu_data->perf_ctrls.desired_perf; > + return 0; > > return (reference_perf * delta_delivered) / delta_reference; > } > @@ -748,18 +751,32 @@ static unsigned int cppc_cpufreq_get_rate(unsigned int cpu) > > ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t0); > if (ret) > - return 0; > + goto out_err; > > udelay(2); /* 2usec delay between sampling */ > > ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t1); > if (ret) > - return 0; > + goto out_err; > > delivered_perf = cppc_perf_from_fbctrs(cpu_data, &fb_ctrs_t0, > &fb_ctrs_t1); You need a check here for !delivered_perf (when at least one of the deltas is 0) in which case it would be good to take the same error path below. Something like: if(delivered_perf) return cppc_perf_to_khz(&cpu_data->perf_caps, delivered_perf); else ret = -EFAULT; That's why I did the tricky if/else dance above as we need to take the error path below for multiple cases. Thanks, Ionela. > > return cppc_perf_to_khz(&cpu_data->perf_caps, delivered_perf); > + > +out_err: > + /* > + * Feedback counters could be 0 when cores are powered down. > + * Take desired perf for reflecting frequency in this case. > + */ > + if (ret == -EFAULT) { > + if (cppc_get_desired_perf(cpu, &delivered_perf)) > + delivered_perf = cpu_data->perf_ctrls.desired_perf; > + > + return cppc_perf_to_khz(&cpu_data->perf_caps, delivered_perf); > + } > + > + return 0; > } > > static int cppc_cpufreq_set_boost(struct cpufreq_policy *policy, int state) > --- > > Thanks indeed! > Jie