Subject: Re: [PATCH] cpufreq: Select schedutil when using big.LITTLE

From: Sudeep Holla <[email-masked]>
Date: Thu, 2 Apr 2020 10:14:55 +0100

On Thu, Apr 02, 2020 at 10:02:39AM +0200, Linus Walleij wrote:
> When we are using a system with big.LITTLE HMP
> configuration, we need to use EAS to schedule the
> system.
> 
> As can be seen from kernel/sched/topology.c:
> 
>  "EAS can be used on a root domain if it meets all the following conditions:
>   1. an Energy Model (EM) is available;
>   2. the SD_ASYM_CPUCAPACITY flag is set in the sched_domain hierarchy.
>   3. no SMT is detected.
>   4. the EM complexity is low enough to keep scheduling overheads low;
>   5. schedutil is driving the frequency of all CPUs of the rd;"
> 
> This means that at the very least, schedutil needs to be
> available as a scheduling policy for EAS to work on these
> systems. Make this explicit by defaulting to the schedutil
> governor if BIG_LITTLE is selected.
> 
> Currently users of the TC2 board (like me) has to figure these
> dependencies out themselves and it is not helpful.
> 
> Suggested-by: Arnd Bergmann <[email-masked]>
> Cc: Vincent Guittot <[email-masked]>
> Cc: Viresh Kumar <[email-masked]>
> Cc: Sudeep Holla <[email-masked]>

Good to see another user of TC2 ;)

FWIW:
Acked-by: Sudeep Holla <[email-masked]>

-- 
Regards,
Sudeep

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