Re: [PATCH 5/6] sched/fair: Consider the idle state of the whole core for load balance

[Peter Zijlstra]

On Thu, May 04, 2023 at 09:09:55AM -0700, Tim Chen wrote:

> @@ -10709,11 +10709,26 @@ static int should_we_balance(struct lb_env *env)
>  	for_each_cpu_and(cpu, group_balance_mask(sg), env->cpus) {
>  		if (!idle_cpu(cpu))
>  			continue;
> +		else {
> +			/*
> +			 * Don't balance to idle SMT in busy core right away when
> +			 * balancing cores, but remember the first idle SMT CPU for
> +			 * later consideration.  Find CPU on an idle core first.
> +			 */
> +			if (!(env->sd->flags & SD_SHARE_CPUCAPACITY) && !is_core_idle(cpu)) {
> +				if (idle_smt == -1)
> +					idle_smt = cpu;
> +				continue;
> +			}
> +		}

Not only does that bust CodingStyle, it's also entirely daft. What
exactly is the purpose of that else statement?

>  
>  		/* Are we the first idle CPU? */
>  		return cpu == env->dst_cpu;
>  	}