Re: [PATCH v6 04/16] sched/core: uclamp: Add CPU's clamp buckets refcounting

[Peter Zijlstra]

On Tue, Jan 15, 2019 at 10:15:01AM +0000, Patrick Bellasi wrote:
> +#ifdef CONFIG_UCLAMP_TASK

> +struct uclamp_bucket {
> +	unsigned long value : bits_per(SCHED_CAPACITY_SCALE);
> +	unsigned long tasks : BITS_PER_LONG - bits_per(SCHED_CAPACITY_SCALE);
> +};

> +struct uclamp_cpu {
> +	unsigned int value;

	/* 4 byte hole */

> +	struct uclamp_bucket bucket[UCLAMP_BUCKETS];
> +};

With the default of 5, this UCLAMP_BUCKETS := 6, so struct uclamp_cpu
ends up being 7 'unsigned long's, or 56 bytes on 64bit (with a 4 byte
hole).

> +#endif /* CONFIG_UCLAMP_TASK */
> +
>  /*
>   * This is the main, per-CPU runqueue data structure.
>   *
> @@ -835,6 +879,11 @@ struct rq {
>  	unsigned long		nr_load_updates;
>  	u64			nr_switches;
>  
> +#ifdef CONFIG_UCLAMP_TASK
> +	/* Utilization clamp values based on CPU's RUNNABLE tasks */
> +	struct uclamp_cpu	uclamp[UCLAMP_CNT] ____cacheline_aligned;

Which makes this 112 bytes with 8 bytes in 2 holes, which is short of 2
64 byte cachelines.

Is that the best layout?

> +#endif
> +
>  	struct cfs_rq		cfs;
>  	struct rt_rq		rt;
>  	struct dl_rq		dl;
> -- 
> 2.19.2
>