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Message-ID: <379e4d1b-9b3b-dc83-99b4-e2a179395733@intel.com>
Date: Wed, 30 Nov 2022 16:35:52 -0800
From: Reinette Chatre <reinette.chatre@...el.com>
To: <babu.moger@....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
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@....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.
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.
Reinette
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