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Date: Wed, 30 Nov 2022 14:40:03 -0600
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>, corbet@....net,
tglx@...utronix.de, mingo@...hat.com, bp@...en8.de
Cc: fenghua.yu@...el.com, dave.hansen@...ux.intel.com, x86@...nel.org,
hpa@...or.com, paulmck@...nel.org, akpm@...ux-foundation.org,
quic_neeraju@...cinc.com, rdunlap@...radead.org,
damien.lemoal@...nsource.wdc.com, songmuchun@...edance.com,
peterz@...radead.org, jpoimboe@...nel.org, pbonzini@...hat.com,
chang.seok.bae@...el.com, pawan.kumar.gupta@...ux.intel.com,
jmattson@...gle.com, daniel.sneddon@...ux.intel.com,
sandipan.das@....com, tony.luck@...el.com, james.morse@....com,
linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
bagasdotme@...il.com, eranian@...gle.com
Subject: Re: [PATCH v8 05/13] x86/resctrl: Detect and configure Slow Memory
Bandwidth Allocation
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@....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
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