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[180.214.233.79]) by smtp.gmail.com with ESMTPSA id v1-20020a1709029a0100b001897e2fd65dsm3119669plp.9.2022.12.17.01.53.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 17 Dec 2022 01:53:18 -0800 (PST) Received: by debian.me (Postfix, from userid 1000) id 53765100B3E; Sat, 17 Dec 2022 16:53:15 +0700 (WIB) Date: Sat, 17 Dec 2022 16:53:15 +0700 From: Bagas Sanjaya To: Qais Yousef , Ingo Molnar , Peter Zijlstra , Vincent Guittot , Dietmar Eggemann , Jonathan Corbet Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Linux ARM , Lukasz Luba , Xuewen Yan , Wei Wang , Jonathan JMChen , Hank , Paul Bone , Russell King , Linus Walleij , Catalin Marinas Subject: Re: [PATCH v3] Documentation: sched: Document util clamp feature Message-ID: References: <20221216235716.201923-1-qyousef@layalina.io> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="IAbXMJJDJGhLPlUP" Content-Disposition: inline In-Reply-To: <20221216235716.201923-1-qyousef@layalina.io> Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org --IAbXMJJDJGhLPlUP Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri, Dec 16, 2022 at 11:57:16PM +0000, Qais Yousef wrote: > +Another example is in Android where tasks are classified as background, > +foreground, top-app, etc. Util clamp can be used to constrain how much > +resources background tasks are consuming by capping the performance poin= t they > +can run at. This constraint helps reserve resources for important tasks,= like > +the ones belonging to the currently active app (top-app group). Beside t= his > +helps in limiting how much power they consume. This can be more obvious = in > +heterogeneous systems (e.g. Arm big.LITTLE); the constraint will help bi= as the > +background tasks to stay on the little cores which will ensure that: > + > + 1. The big cores are free to run top-app tasks immediately. top-= app > + tasks are the tasks the user is currently interacting with, h= ence > + the most important tasks in the system. > + 2. They don't run on a power hungry core and drain battery even = if they > + are CPU intensive tasks. > + > +.. note:: > + **little cores**: > + CPUs with capacity < 1024 > + > + **big cores**: > + CPUs with capacity =3D 1024 Processing capacity (CPU frequency) in MHz? This is the first time I hear Arm big.LITTLE architecture. CC'ing several Arm folks and linux-arm-kernel list for I'm unsure on this. > + > +By making these uclamp performance requests, or rather hints, user space= can > +ensure system resources are used optimally to deliver the best possible = user > +experience. > + > +Another use case is to help with **overcoming the ramp up latency inheri= t in > +how scheduler utilization signal is calculated**. IMO the bold text isn't needed (why did you highlight the phrase above)? > +When task @p is running, **the scheduler should try its best to ensure it > +starts at 40% performance level**. If the task runs for a long enough ti= me so > +that its actual utilization goes above 80%, the utilization, or performa= nce > +level, will be capped. Same here. > +**Generally it is advised to perceive the input as performance level or = point > +which will imply both task placement and frequency selection**. Same here too. Thanks. --=20 An old man doll... just what I always wanted! - Clara --IAbXMJJDJGhLPlUP Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYIAB0WIQSSYQ6Cy7oyFNCHrUH2uYlJVVFOowUCY52ReQAKCRD2uYlJVVFO o4HkAP4rc8AULhBHVO7Y9cRRRNKL0KVpwku8TWCuK0K3HNSBjgEAmNGvg6da34fs mfQfANrw8H/CE0iusS8NXjKKCrYFugk= =tqHd -----END PGP SIGNATURE----- --IAbXMJJDJGhLPlUP--