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 point 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 this > +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 bias 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, hence > + 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 = 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 inherit 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 time so > +that its actual utilization goes above 80%, the utilization, or performance > +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. -- An old man doll... just what I always wanted! - Clara
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