linux-kernel - Re: [PATCH v4 08/18] x86/intel_rdt: Pick up L3/L2 RDT parameters from CPUID

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Date:   Mon, 17 Oct 2016 11:06:55 -0700
From:   Fenghua Yu <fenghua.yu@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Fenghua Yu <fenghua.yu@...el.com>,
        "H. Peter Anvin" <h.peter.anvin@...el.com>,
        Ingo Molnar <mingo@...e.hu>, Tony Luck <tony.luck@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Stephane Eranian <eranian@...gle.com>,
        Borislav Petkov <bp@...e.de>,
        Dave Hansen <dave.hansen@...el.com>,
        Nilay Vaish <nilayvaish@...il.com>, Shaohua Li <shli@...com>,
        David Carrillo-Cisneros <davidcc@...gle.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        Sai Prakhya <sai.praneeth.prakhya@...el.com>,
        Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v4 08/18] x86/intel_rdt: Pick up L3/L2 RDT parameters
 from CPUID

On Mon, Oct 17, 2016 at 03:45:32PM +0200, Thomas Gleixner wrote:
> On Fri, 14 Oct 2016, Fenghua Yu wrote:
> > +/**
> > + * struct rdt_resource - attributes of an RDT resource
> > + * @enabled:			Is this feature enabled on this machine
> > + * @name:			Name to use in "schemata" file
> > + * @max_closid:			Maximum number of CLOSIDs supported
> > + * @num_closid:			Current number of CLOSIDs available
> > + * @max_cbm:			Largest Cache Bit Mask allowed
> > + * @min_cbm_bits:		Minimum number of bits to be set in a cache
> 
> That should be 'number of consecutive bits', right?

Change to "Minimum number of consecutive bits to be set in a cache", is
that ok?

It's 2 on Haswell. It's 1 in other cases i.e. L3 on Broadwell and
Skylake servers etc.

> 
> > + *				bit mask
> > + * @domains:			All domains for this resource
> > + * @num_domains:		Number of domains active
> > + * @msr_base:			Base MSR address for CBMs
> > + * @cdp_capable:		Code/Data Prioritization available
> > + * @cdp_enabled:		Code/Data Prioritization enabled
> 
> I wonder whether this is the proper abstraction level. We might as well do
> the following:
> 
> rdtresources[] = {
>      {
> 	.name	= "L3",
>      },
>      {
> 	.name	= "L3Data",
>      },
>      {
> 	.name	= "L3Code",
>      },
> 
> and enable either L3 or L3Data+L3Code. Not sure if that makes things
> simpler, but it's definitely worth a thought or two.

This way will be better than having cdp_enabled/capable for L3 and not
for L2.  And this doesn't change current userinterface design either,
I think.

> 
> > +#define for_each_rdt_resource(r)	\
> > +	for (r = rdt_resources_all; r->name; r++) \
> > +		if (r->enabled)
> 
> So the resource array must be NULL terminated, right? You might as well use
> 
>    r < rdt_resources_all + ARRAY_SIZE(rdt_resources_all)
> 
> as the loop condition. So you avoid the NULL termination.

Will do.

> 
> > +
> > +#define IA32_L3_CBM_BASE	0xc90
> > +extern struct rdt_resource rdt_resources_all[];
> 
> Please visually split this. CBM_BASE has nothing to do with the resource
> array.
> 
> > +#define domain_init(name) LIST_HEAD_INIT(rdt_resources_all[name].domains)
> 
> name is really misleading here. Please use id and make this an inline
> function.
> 
> > +struct rdt_resource rdt_resources_all[] = {
> 
> >  static inline bool get_rdt_resources(void)
> >  {
> > +	struct rdt_resource *r;
> >  	bool ret = false;
> >  
> >  	if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL &&
> > @@ -74,20 +105,53 @@ static inline bool get_rdt_resources(void)
> >  
> >  	if (!boot_cpu_has(X86_FEATURE_RDT_A))
> >  		return false;
> > -	if (boot_cpu_has(X86_FEATURE_CAT_L3))
> > +	if (boot_cpu_has(X86_FEATURE_CAT_L3)) {
> > +		union cpuid_0x10_1_eax eax;
> > +		union cpuid_0x10_1_edx edx;
> > +		u32 ebx, ecx;
> > +
> > +		r = &rdt_resources_all[RDT_RESOURCE_L3];
> > +		cpuid_count(0x00000010, 1, &eax.full, &ebx, &ecx, &edx.full);
> > +		r->max_closid = edx.split.cos_max + 1;
> > +		r->num_closid = r->max_closid;
> > +		r->cbm_len = eax.split.cbm_len + 1;
> > +		r->max_cbm = BIT_MASK(eax.split.cbm_len + 1) - 1;
> > +		if (boot_cpu_has(X86_FEATURE_CDP_L3))
> > +			r->cdp_capable = true;
> > +		r->enabled = true;
> > +
> >  		ret = true;
> > +	}
> > +	if (boot_cpu_has(X86_FEATURE_CAT_L2)) {
> > +		union cpuid_0x10_1_eax eax;
> > +		union cpuid_0x10_1_edx edx;
> > +		u32 ebx, ecx;
> > +
> > +		/* CPUID 0x10.2 fields are same format at 0x10.1 */
> > +		r = &rdt_resources_all[RDT_RESOURCE_L2];
> > +		cpuid_count(0x00000010, 2, &eax.full, &ebx, &ecx, &edx.full);
> > +		r->max_closid = edx.split.cos_max + 1;
> > +		r->num_closid = r->max_closid;
> > +		r->cbm_len = eax.split.cbm_len + 1;
> > +		r->max_cbm = BIT_MASK(eax.split.cbm_len + 1) - 1;
> > +		r->enabled = true;
> 
> Copy and paste is a wonderful thing, right?
> 
> static void rdt_get_config(int idx, struct rdt_resource *r)
> {
> 	union cpuid_0x10_1_eax eax;
> 	union cpuid_0x10_1_edx edx;
> 	u32 ebx, ecx;
> 
> 	cpuid_count(0x00000010, idx, &eax.full, &ebx, &ecx, &edx.full);
> 	r->max_closid = edx.split.cos_max + 1;
> 	r->num_closid = r->max_closid;
> 	r->cbm_len = eax.split.cbm_len + 1;
> 	r->max_cbm = BIT_MASK(eax.split.cbm_len + 1) - 1;
> 	r->enabled = true;
> }
> 
> and and the call site:
> 
> 	if (boot_cpu_has(X86_FEATURE_CAT_L3)) {
> 		rdt_get_config(1, &rdt_resources_all[RDT_RESOURCE_L3]);
> 		if (boot_cpu_has(X86_FEATURE_CDP_L3))
> 			r->cdp_capable = true;
> 		ret = true;
> 	}
> 
> 	if (boot_cpu_has(X86_FEATURE_CAT_L2)) {
> 		rdt_get_config(2, &rdt_resources_all[RDT_RESOURCE_L2]);
> 		ret = true;
> 	}
> 
> Hmm?

Sure.

Thanks.

-Fenghua