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

[Moger, Babu]

[AMD Official Use Only - General]

Hi Reinette,

> -----Original Message-----
> From: Reinette Chatre <reinette.chatre@xxxxxxxxx>
> Sent: Wednesday, November 30, 2022 6:36 PM
> To: Moger, Babu <Babu.Moger@xxxxxxx>; corbet@xxxxxxx;
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> Subject: Re: [PATCH v8 05/13] x86/resctrl: Detect and configure Slow Memory
> Bandwidth Allocation
> 
> Hi Babu,
> 
> On 11/30/2022 12:40 PM, Moger, Babu wrote:
> > On 11/30/22 14:07, Reinette Chatre wrote:
> >> 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@xxxxxxx>
> >>>>> ---
> >>>>>  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.
> 
> I agree that this is not a strong argument. If this happens then Intel can split the
> initialization also. This is also not the only bits that would need changing since
> only __rdt_get_mem_config_amd() can initialize an SMBA resource.
> 
> It does not sound like there is a clear winner. To answer your earlier question
> more succinctly, yes, from my perspective you can keep the change to
> rdt_init_res_defs_amd(). At least with this change things would be more
> familiar between MBA and SMBA and it will be obvious that SMBA is not
> supported by Intel.

Will do. Thanks
Babu

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