From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f169.google.com (mail-pl1-f169.google.com [209.85.214.169]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 626D23596F; Thu, 10 Apr 2025 01:52:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.169 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744249948; cv=none; b=ZB5gPxm3JeTV12cKiRf1w0WKjDpeT/si4ZSoawsg2VbEjBqoOd/e4MHWZbCz/fN2XD6b3J3d9fNd06kmTN0/bFW7kNhvVrMUutccctdh+MqfhowCmHoPdRCUUvY3DfU7ynVRnShq2WLvLku8K/ATTmD56FDCqV8bi7t84UC9DQY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744249948; c=relaxed/simple; bh=vKLzshF1zBPzzTMXiGt8BdyQZzHIDPA5ufOZaf1gACk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=I/ieysIhYXTVRH8l6BuaH/9upOUGY6dSfXVlxcYcyVFGZDUTVzr5jFM1tVYYsY+XgbxQfZA0ijYhvdk4p9qiu4Rr24KLN0GTxnicgZnXwY1fdrrBaNEeV3z1lBJyhYJdOmfOE2hn5EbhyhRSDfG58P+0+jZPEJO3wqEw7jiSZuo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=kerneltoast.com; spf=pass smtp.mailfrom=gmail.com; arc=none smtp.client-ip=209.85.214.169 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=kerneltoast.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Received: by mail-pl1-f169.google.com with SMTP id d9443c01a7336-2254e0b4b79so3792565ad.2; Wed, 09 Apr 2025 18:52:25 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1744249944; x=1744854744; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=jaJxqLk3V06ArQnoQFKz5rLPJR/azvazadpvaNzDZW8=; b=PQIEkQX0ucShjrpg8ZrCh+3wri4vk5AToyfIAtrkQ58fdieZdfDlQBhY0mjpycrmcP OLJJl5HhFYGmTu1Qz17edVMf9c9ffNHrBlDAZoUbdOqYy/S/B0WhK0MfgpGVzfkVWk4a UTRRpjpmcq/XZWyDicmMrnH4HgnPs36O+WFrxZyo+0uytkP5a6B4USJWYLDycJBW0lkk +id/P0Ool00T+j+P90PBN+nYJ3UEosbgvW8KcaLXzoSxSxYBgnHekrXmSFmYTUGgy+Pu qeqykfog2P1br3hLK2/4o4iP1/jsAELGkVuuYzt3+98K4bVraxxzNPaYBncCvimemrZc M0Dg== X-Forwarded-Encrypted: i=1; AJvYcCUVvwoWoIMCYI1DEL6eI0sfTb7PluPnLIg6HaIR/i+OSn0skz/+Iphf72/vjH+VWe2ihzwdASHfNBp61Pc=@vger.kernel.org, AJvYcCXkXWxeP4dADW52GAk8bhvNHYiGUnXJ/nf7LJKpfU4JISYKcO44UoxjB4eGcDGJwKCBYMrBec+RQf0=@vger.kernel.org X-Gm-Message-State: AOJu0YzbBqVmlSdRg3cVc1A8Y8PL+0QIEdYa4jldji4yE+6Corf1NZUu LUqBvdPf6y6yqoU1En+NvncGnftyWtE0S2wDqRsmn79AAPopzKbe X-Gm-Gg: ASbGnctULVsmlToqsvGJXC4uKNXmQc7Urqgzh/1o6/Ty5PilbI6B2SC75/NkiqRBf1i 80rbmX/9KyX8m705RMsOru5ApToS8J1txAWQmZZCmAQ/VrT4U/Nhr1JIahmFLWpaNi25dz/tPW9 6ZR+mfu1FAygSI8YmTCDD8n1C8l2S8rz+hASjOHcW5QVPqVQYhTACuYk6gSktNi4TZQN7uK2Zsm wpYNOy62Jtl8GtjYH742rWp7TF2O9x5iZatmKlztwMx7CvYTVE2wEQISwb1Kg7tB1n2CInSrEcj Y830VfmJhcJRBA6pJjcoYFlm2fNhvzCRsLv52m72F4IgPw5urhJEOIpT0aI= X-Google-Smtp-Source: AGHT+IH5DMA8QYKm1WbSD1sLTN8mlWGKoMcvZflMV5qQELvdqIA+8gtpJaS3iupJUAV6K+BCGVRtRg== X-Received: by 2002:a17:902:f64d:b0:21f:164d:93fe with SMTP id d9443c01a7336-22be04199b5mr8933505ad.53.1744249944613; Wed, 09 Apr 2025 18:52:24 -0700 (PDT) Received: from sultan-box.localdomain ([142.147.89.201]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-306dd10dc40sm2679257a91.9.2025.04.09.18.52.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 09 Apr 2025 18:52:24 -0700 (PDT) Date: Wed, 9 Apr 2025 18:52:20 -0700 From: Sultan Alsawaf To: Stephan Gerhold Cc: "Rafael J. Wysocki" , Viresh Kumar , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, regressions@lists.linux.dev, Johan Hovold Subject: Re: [PATCH 1/2] cpufreq: schedutil: Fix superfluous updates caused by need_freq_update Message-ID: References: <20241212015734.41241-1-sultan@kerneltoast.com> <20241212015734.41241-2-sultan@kerneltoast.com> Precedence: bulk X-Mailing-List: linux-kernel@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: On Tue, Apr 08, 2025 at 06:48:06PM +0200, Stephan Gerhold wrote: > Hi Sultan, > > On Tue, Apr 08, 2025 at 08:22:20AM -0700, Sultan Alsawaf wrote: > > On Tue, Apr 08, 2025 at 10:59:31AM +0200, Stephan Gerhold wrote: > > > On Wed, Dec 11, 2024 at 05:57:32PM -0800, Sultan Alsawaf wrote: > > > > From: "Sultan Alsawaf (unemployed)" > > > > > > > > A redundant frequency update is only truly needed when there is a policy > > > > limits change with a driver that specifies CPUFREQ_NEED_UPDATE_LIMITS. > > > > > > > > In spite of that, drivers specifying CPUFREQ_NEED_UPDATE_LIMITS receive a > > > > frequency update _all the time_, not just for a policy limits change, > > > > because need_freq_update is never cleared. > > > > > > > > Furthermore, ignore_dl_rate_limit()'s usage of need_freq_update also leads > > > > to a redundant frequency update, regardless of whether or not the driver > > > > specifies CPUFREQ_NEED_UPDATE_LIMITS, when the next chosen frequency is the > > > > same as the current one. > > > > > > > > Fix the superfluous updates by only honoring CPUFREQ_NEED_UPDATE_LIMITS > > > > when there's a policy limits change, and clearing need_freq_update when a > > > > requisite redundant update occurs. > > > > > > > > This is neatly achieved by moving up the CPUFREQ_NEED_UPDATE_LIMITS test > > > > and instead setting need_freq_update to false in sugov_update_next_freq(). > > > > > > > > Signed-off-by: Sultan Alsawaf (unemployed) > > > > --- > > > > kernel/sched/cpufreq_schedutil.c | 4 ++-- > > > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > > > > > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c > > > > index 28c77904ea74..e51d5ce730be 100644 > > > > --- a/kernel/sched/cpufreq_schedutil.c > > > > +++ b/kernel/sched/cpufreq_schedutil.c > > > > @@ -83,7 +83,7 @@ static bool sugov_should_update_freq(struct sugov_policy *sg_policy, u64 time) > > > > > > > > if (unlikely(sg_policy->limits_changed)) { > > > > sg_policy->limits_changed = false; > > > > - sg_policy->need_freq_update = true; > > > > + sg_policy->need_freq_update = cpufreq_driver_test_flags(CPUFREQ_NEED_UPDATE_LIMITS); > > > > return true; > > > > } > > > > > > > > @@ -96,7 +96,7 @@ static bool sugov_update_next_freq(struct sugov_policy *sg_policy, u64 time, > > > > unsigned int next_freq) > > > > { > > > > if (sg_policy->need_freq_update) > > > > - sg_policy->need_freq_update = cpufreq_driver_test_flags(CPUFREQ_NEED_UPDATE_LIMITS); > > > > + sg_policy->need_freq_update = false; > > > > else if (sg_policy->next_freq == next_freq) > > > > return false; > > > > > > > > > > This patch breaks cpufreq throttling (e.g. for thermal cooling) for > > > cpufreq drivers that: > > > > > > - Have policy->fast_switch_enabled/fast_switch_possible set, but > > > - Do not have CPUFREQ_NEED_UPDATE_LIMITS flag set > > > > > > There are several examples for this in the tree (search for > > > "fast_switch_possible"). Of all those drivers, only intel-pstate and > > > amd-pstate (sometimes) set CPUFREQ_NEED_UPDATE_LIMITS. > > > > > > I can reliably reproduce this with scmi-cpufreq on a Qualcomm X1E > > > laptop: > > > > > > 1. I added some low temperature trip points in the device tree, > > > together with passive cpufreq cooling. > > > 2. I run a CPU stress test on all CPUs and monitor the temperatures > > > and CPU frequencies. > > > > > > When using "performance" governor instead of "schedutil", the CPU > > > frequencies are being throttled as expected, as soon as the temperature > > > trip points are reached. > > > > > > When using "schedutil", the CPU frequencies stay at maximum as long as > > > the stress test is running. No throttling happens, so the device heats > > > up far beyond the defined temperature trip points. Throttling is applied > > > only after stopping the stress test, since this forces schedutil to > > > re-evaluate the CPU frequency. > > > > > > Reverting this commit fixes the problem. > > > > > > Looking at the code, I think the problem is that: > > > - sg_policy->limits_changed does not result in > > > sg->policy->need_freq_update without CPUFREQ_NEED_UPDATE_LIMITS > > > anymore, and > > > - Without sg->policy->need_freq_update, get_next_freq() skips calling > > > cpufreq_driver_resolve_freq(), which would normally apply the policy > > > min/max constraints. > > > > > > Do we need to set CPUFREQ_NEED_UPDATE_LIMITS for all cpufreq drivers > > > that set policy->fast_switch_possible? If I'm reading the documentation > > > comment correctly, that flag is just supposed to enable notifications if > > > the policy min/max changes, but the resolved target frequency is still > > > the same. This is not the case here, the target frequency needs to be > > > throttled, but schedutil isn't applying the new limits. > > > > > > Any suggestions how to fix this? I'm happy to test patches with my > > > setup. > > > > Thank you for reporting this. As I see it, sg_policy->need_freq_update is > > working correctly now; however, sg_policy->limits_changed relied on the broken > > behavior of sg_policy->need_freq_update and therefore sg_policy->limits_changed > > needs to be fixed. > > Thanks for the quick reply and the patch! > > > > > Can you try this patch: > > > > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c > > index 1a19d69b91ed3..f37b999854d52 100644 > > --- a/kernel/sched/cpufreq_schedutil.c > > +++ b/kernel/sched/cpufreq_schedutil.c > > @@ -82,7 +82,6 @@ static bool sugov_should_update_freq(struct sugov_policy *sg_policy, u64 time) > > return false; > > > > if (unlikely(sg_policy->limits_changed)) { > > - sg_policy->limits_changed = false; > > sg_policy->need_freq_update = cpufreq_driver_test_flags(CPUFREQ_NEED_UPDATE_LIMITS); > > return true; > > } > > @@ -171,9 +170,11 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy, > > freq = get_capacity_ref_freq(policy); > > freq = map_util_freq(util, freq, max); > > > > - if (freq == sg_policy->cached_raw_freq && !sg_policy->need_freq_update) > > + if (freq == sg_policy->cached_raw_freq && !sg_policy->limits_changed && > > + !sg_policy->need_freq_update) > > return sg_policy->next_freq; > > > > + sg_policy->limits_changed = false; > > sg_policy->cached_raw_freq = freq; > > return cpufreq_driver_resolve_freq(policy, freq); > > } > > > > This is working correctly for me, CPU frequency is being throttled again > when the temperature trip points are reached. Great to hear, thanks for testing that so quickly! > If you send this, feel free to add: > > Tested-by: Stephan Gerhold I'll do Reported-and-tested-by if you don't mind. :-) > > Thanks! > Stephan Thanks, Sultan