linux-kernel - Re: [PATCH 4/8] x86/intel_rct/mba: Add MBA structures and initialize MBA

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Date:   Wed, 5 Apr 2017 17:40:35 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Vikas Shivappa <vikas.shivappa@...ux.intel.com>
cc:     vikas.shivappa@...el.com, x86@...nel.org,
        linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
        peterz@...radead.org, ravi.v.shankar@...el.com,
        tony.luck@...el.com, fenghua.yu@...el.com, h.peter.anvin@...el.com
Subject: Re: [PATCH 4/8] x86/intel_rct/mba: Add MBA structures and initialize
 MBA

On Mon, 3 Apr 2017, Vikas Shivappa wrote:
>  
>  /**
> + * struct rdt_domain - group of cpus sharing an RDT resource
> + * @list:	all instances of this resource
> + * @id:		unique id for this instance
> + * @cpu_mask:	which cpus share this resource
> + * @ctrl_val:	array of cache or mem ctrl values (indexed by CLOSID)
> + * @new_cbm:	new cbm value to be loaded
> + * @have_new_cbm: did user provide new_cbm for this domain

The version which you removed below has the kernel-doc comments correct ....

> +/**
>   * struct rdt_resource - attributes of an RDT resource
>   * @enabled:			Is this feature enabled on this machine
>   * @capable:			Is this feature available on this machine
> @@ -78,6 +109,16 @@ struct rftype {
>   * @data_width:		Character width of data when displaying
>   * @min_cbm_bits:		Minimum number of consecutive bits to be set
>   *				in a cache bit mask
> + * @msr_update:		Function pointer to update QOS MSRs
> + * @max_delay:			Max throttle delay. Delay is the hardware
> + *				understandable value for memory bandwidth.
> + * @min_bw:			Minimum memory bandwidth percentage user
> + *				can request
> + * @bw_gran:			Granularity at which the memory bandwidth
> + *				is allocated
> + * @delay_linear:		True if memory b/w delay is in linear scale
> + * @mb_map:			Mapping of memory b/w percentage to
> + *				memory b/w delay values
>   * @domains:			All domains for this resource
>   * @msr_base:			Base MSR address for CBMs
>   * @cache_level:		Which cache level defines scope of this domain
> @@ -94,6 +135,14 @@ struct rdt_resource {
>  	int			min_cbm_bits;
>  	u32			default_ctrl;
>  	int			data_width;
> +	void (*msr_update)	(struct rdt_domain *d, struct msr_param *m,
> +				 struct rdt_resource *r);
> +	u32			max_delay;
> +	u32			min_bw;
> +	u32			bw_gran;
> +	u32			delay_linear;
> +	u32			*mb_map;

I don't know what other weird controls will be added over time, but we are
probably better off to have

struct cache_ctrl {
	int		cbm_len;
	int		min_cbm_bits;
};

struct mba_ctrl {
	u32			max_delay;
	u32			min_bw;
	u32			bw_gran;
	u32			delay_linear;
	u32			*mb_map;
};

and in then in struct rdt_resource:

       <common fields>
       union {
       		struct cache_ctrl	foo;
		struct mba_ctrl		bla;
	} ctrl;


That avoids that rdt_resource becomes a hodgepodge of unrelated or even
contradicting fields.

Hmm?

Thanks,

	tglx