Re: [PATCH v8 05/13] x86/resctrl: Detect and configure Slow Memory Bandwidth Allocation

["Moger, Babu" <babu.moger@amd.com>]

On 11/30/22 14:07, Reinette Chatre wrote:
> Hi Babu,
>
> On 11/30/2022 10:43 AM, Moger, Babu wrote:
>> On 11/22/22 18:12, Reinette Chatre wrote:
>>> On 11/4/2022 1:00 PM, Babu Moger wrote:
>>>> The QoS slow memory configuration details are available via
>>>> CPUID_Fn80000020_EDX_x02. Detect the available details and
>>>> initialize the rest to defaults.
>>>>
>>>> Signed-off-by: Babu Moger <babu.moger@amd.com>
>>>> ---
>>>>  arch/x86/kernel/cpu/resctrl/core.c        |   36 +++++++++++++++++++++++++++--
>>>>  arch/x86/kernel/cpu/resctrl/ctrlmondata.c |    2 +-
>>>>  arch/x86/kernel/cpu/resctrl/internal.h    |    1 +
>>>>  arch/x86/kernel/cpu/resctrl/rdtgroup.c    |    8 ++++--
>>>>  4 files changed, 41 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
>>>> index e31c98e2fafc..6571d08e2b0d 100644
>>>> --- a/arch/x86/kernel/cpu/resctrl/core.c
>>>> +++ b/arch/x86/kernel/cpu/resctrl/core.c
>>>> @@ -162,6 +162,13 @@ bool is_mba_sc(struct rdt_resource *r)
>>>>  	if (!r)
>>>>  		return rdt_resources_all[RDT_RESOURCE_MBA].r_resctrl.membw.mba_sc;
>>>>  
>>>> +	/*
>>>> +	 * The software controller support is only applicable to MBA resource.
>>>> +	 * Make sure to check for resource type again.
>>>> +	 */
>>> /again/d
>>>
>>> Not all callers of is_mba_sc() check if it is called for an MBA resource.
>>>
>>>> +	if (r->rid != RDT_RESOURCE_MBA)
>>>> +		return false;
>>>> +
>>>>  	return r->membw.mba_sc;
>>>>  }
>>>>  
>>>> @@ -225,9 +232,15 @@ static bool __rdt_get_mem_config_amd(struct rdt_resource *r)
>>>>  	struct rdt_hw_resource *hw_res = resctrl_to_arch_res(r);
>>>>  	union cpuid_0x10_3_eax eax;
>>>>  	union cpuid_0x10_x_edx edx;
>>>> -	u32 ebx, ecx;
>>>> +	u32 ebx, ecx, subleaf;
>>>>  
>>>> -	cpuid_count(0x80000020, 1, &eax.full, &ebx, &ecx, &edx.full);
>>>> +	/*
>>>> +	 * Query CPUID_Fn80000020_EDX_x01 for MBA and
>>>> +	 * CPUID_Fn80000020_EDX_x02 for SMBA
>>>> +	 */
>>>> +	subleaf = (r->rid == RDT_RESOURCE_SMBA) ? 2 :  1;
>>>> +
>>>> +	cpuid_count(0x80000020, subleaf, &eax.full, &ebx, &ecx, &edx.full);
>>>>  	hw_res->num_closid = edx.split.cos_max + 1;
>>>>  	r->default_ctrl = MAX_MBA_BW_AMD;
>>>>  
>>>> @@ -750,6 +763,19 @@ static __init bool get_mem_config(void)
>>>>  	return false;
>>>>  }
>>>>  
>>>> +static __init bool get_slow_mem_config(void)
>>>> +{
>>>> +	struct rdt_hw_resource *hw_res = &rdt_resources_all[RDT_RESOURCE_SMBA];
>>>> +
>>>> +	if (!rdt_cpu_has(X86_FEATURE_SMBA))
>>>> +		return false;
>>>> +
>>>> +	if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD)
>>>> +		return __rdt_get_mem_config_amd(&hw_res->r_resctrl);
>>>> +
>>>> +	return false;
>>>> +}
>>>> +
>>>>  static __init bool get_rdt_alloc_resources(void)
>>>>  {
>>>>  	struct rdt_resource *r;
>>>> @@ -780,6 +806,9 @@ static __init bool get_rdt_alloc_resources(void)
>>>>  	if (get_mem_config())
>>>>  		ret = true;
>>>>  
>>>> +	if (get_slow_mem_config())
>>>> +		ret = true;
>>>> +
>>>>  	return ret;
>>>>  }
>>>>  
>>>> @@ -869,6 +898,9 @@ static __init void rdt_init_res_defs_amd(void)
>>>>  		} else if (r->rid == RDT_RESOURCE_MBA) {
>>>>  			hw_res->msr_base = MSR_IA32_MBA_BW_BASE;
>>>>  			hw_res->msr_update = mba_wrmsr_amd;
>>>> +		} else if (r->rid == RDT_RESOURCE_SMBA) {
>>>> +			hw_res->msr_base = MSR_IA32_SMBA_BW_BASE;
>>>> +			hw_res->msr_update = mba_wrmsr_amd;
>>>>  		}
>>>>  	}
>>>>  }
>>> I mentioned earlier that this can be moved to init of
>>> rdt_resources_all[]. No strong preference, leaving here works
>>> also.
>> I am little confused about this comment. Initialization of
>> rdt_resources_all in core.c is mostly generic initialization. The msr_base
>> and msr_update routines here are vendor specific. I would prefer to keep
>> this in
> This is a contradiction. Yes, rdt_resources_all[] initialization in core.c
> is indeed generic initialization, so why is SMBA there? If this was really
> generic initialization then the entire initialization of SMBA resource
> should rather move to AMD specific code.
>
> SMBA is an AMD only feature yet its resource initialization is fragmented
> with one portion treated as generic and another portion treated as vendor
> specific while it all is vendor specific.
>
> The current fragmentation is not clear to me. Keeping the initialization
> as you have in patch #2 is the simplest and that is what prompted me
> to suggest the move to keep initialization together at that location.
>
>> rdt_init_res_defs_amd.Is that ok?
> The generic vs non-generic initialization argument is not convincing to me. 
> Could you please elaborate why you prefer it this way? I already mentioned
> that I do not have a strong preference but I would like to understand what
> the motivation for this split initialization is.
>
I dont have any strong argument. I was thinking, in case Intel supports
this resource in the future then they only have to change
rdt_init_res_defs_intel.

Thanks

Babu