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[86.128.182.179]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48e3eb8f248sm3795461f8f.6.2026.10.24.04.34.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 24 Oct 2026 04:34:42 -0700 (PDT) Message-ID: Date: Sat, 24 Oct 2026 12:34:41 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: Uclamp races due to non-atomic static_branch_likely updates To: Christian Loehle , Peter Zijlstra Cc: Steven Rostedt , John Stultz , Vincent Guittot , Qais Yousef , LKML , Hongyan Xia , Ingo Molnar , Wei Wang , Patrick Bellasi , Dietmar Eggemann References: <20261020152933.16989549@gandalf.local.home> <20261021113806.GE2823843@noisy.programming.kicks-ass.net> <20261021132058.kxzyumgxzir4jzi2@airbuntu> <20261021132956.GO2823843@noisy.programming.kicks-ass.net> <20261021140222.tazz6aw4j5pvqwox@airbuntu> <005ed941-2737-413c-8436-a9de227d01ca@arm.com> Content-Language: en-US From: Qais Yousef In-Reply-To: <005ed941-2737-413c-8436-a9de227d01ca@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 10/22/26 14:18, Christian Loehle wrote: > So I guess the clear-when-entering-idle taper is sufficient for UCLAMP_MIN. > UCLAMP_MAX (where on a sufficiently low setting we may just never have that > idle entry to clear) we expect to be fine because it's max-aggregated, i.e. > a second task would let us escape the low stale UCLAMP_MAX on the rq? I am not sure I got you. We should eventually go to idle and reset the settings. But you made me realize the unconditional reset could break the saved uclamp max at idle :-/ I could either unconditionally set both uclamp_{min, max} to 0, or just have some conditions to do_once when uclamp_is_used(). I prefer setting to 0, but this is a change in behavior. > I guess we could reevaluate the static branch at every tick too if we really > care? It seems you are worried about the temporary corrupt state after boot (first uclamp use more precisely) where there's no idle time, right? I think we can live with that.