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Date: Wed, 11 Jan 2023 18:39:59 -0600
From: "Moger, Babu" <bmoger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>,
"Moger, Babu" <Babu.Moger@....com>,
"corbet@....net" <corbet@....net>,
"tglx@...utronix.de" <tglx@...utronix.de>,
"mingo@...hat.com" <mingo@...hat.com>,
"bp@...en8.de" <bp@...en8.de>
Cc: "fenghua.yu@...el.com" <fenghua.yu@...el.com>,
"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
"x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
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<pawan.kumar.gupta@...ux.intel.com>,
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Subject: Re: [PATCH v11 13/13] Documentation/x86: Update resctrl.rst for new
features
Hi Reinette,
On 1/11/2023 4:56 PM, Reinette Chatre wrote:
> Hi Babu,
>
> On 1/11/2023 2:39 PM, Moger, Babu wrote:
>> [AMD Official Use Only - General]
>>
>> Hi Reinette,
>>
>>> -----Original Message-----
>>> From: Reinette Chatre <reinette.chatre@...el.com>
>>> Sent: Wednesday, January 11, 2023 4:07 PM
>>> To: Moger, Babu <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; Das1, Sandipan
>>> <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; christophe.leroy@...roup.eu;
>>> jarkko@...nel.org; adrian.hunter@...el.com; quic_jiles@...cinc.com;
>>> peternewman@...gle.com
>>> Subject: Re: [PATCH v11 13/13] Documentation/x86: Update resctrl.rst for new
>>> features
>>>
>>> Hi Babu,
>>>
>>> On 1/9/2023 8:44 AM, Babu Moger wrote:
>>>> Update the documentation for the new features:
>>>> 1. Slow Memory Bandwidth allocation (SMBA).
>>>> With this feature, the QOS enforcement policies can be applied
>>>> to the external slow memory connected to the host. QOS enforcement
>>>> is accomplished by assigning a Class Of Service (COS) to a processor
>>>> and specifying allocations or limits for that COS for each resource
>>>> to be allocated.
>>>>
>>>> 2. Bandwidth Monitoring Event Configuration (BMEC).
>>>> The bandwidth monitoring events mbm_total_bytes and mbm_local_bytes
>>>> are set to count all the total and local reads/writes respectively.
>>>> With the introduction of slow memory, the two counters are not
>>>> enough to count all the different types of memory events. With the
>>>> feature BMEC, the users have the option to configure mbm_total_bytes
>>>> and mbm_local_bytes to count the specific type of events.
>>>>
>>>> Also add configuration instructions with examples.
>>>>
>>>> Signed-off-by: Babu Moger <babu.moger@....com>
>>>> ---
>>>> Documentation/x86/resctrl.rst | 142
>>>> +++++++++++++++++++++++++++++++++-
>>>> 1 file changed, 140 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/Documentation/x86/resctrl.rst
>>>> b/Documentation/x86/resctrl.rst index 71a531061e4e..2860856f4463
>>>> 100644
>>>> --- a/Documentation/x86/resctrl.rst
>>>> +++ b/Documentation/x86/resctrl.rst
>>>> @@ -17,14 +17,16 @@ AMD refers to this feature as AMD Platform Quality
>>> of Service(AMD QoS).
>>>> This feature is enabled by the CONFIG_X86_CPU_RESCTRL and the x86
>>>> /proc/cpuinfo flag bits:
>>>>
>>>> -=============================================
>>> ================================
>>>> +===============================================
>>> ================================
>>>> RDT (Resource Director Technology) Allocation "rdt_a"
>>>> CAT (Cache Allocation Technology) "cat_l3", "cat_l2"
>>>> CDP (Code and Data Prioritization) "cdp_l3", "cdp_l2"
>>>> CQM (Cache QoS Monitoring) "cqm_llc",
>>> "cqm_occup_llc"
>>>> MBM (Memory Bandwidth Monitoring) "cqm_mbm_total",
>>> "cqm_mbm_local"
>>>> MBA (Memory Bandwidth Allocation) "mba"
>>>> -=============================================
>>> ================================
>>>> +SMBA (Slow Memory Bandwidth Allocation) "smba"
>>>> +BMEC (Bandwidth Monitoring Event Configuration) "bmec"
>>>> +===============================================
>>> ================================
>>> I expect that you will follow Boris's guidance here and not make these flags
>>> visible in /proc/cpuinfo. That would imply that this addition will have no entries
>>> in the second column. Perhaps this could be made easier to parse by using
>>> empty quotes ("") in the second column to match syntax used in the existing
>>> flags as well as the cpufeatures.h change?
>> Hmm.. I thought we dropped that idea for now. Did I miss understand that?
> I referred to the guidance in https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Flkml%2FY7xjxUj%2BKnOEJssZ%40zn.tnic%2F&data=05%7C01%7CBabu.Moger%40amd.com%7C900eb41c0e6049dd342208daf4270d2b%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638090745842366944%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=%2F5GVOhnxq1%2B3nJwGtlApvLfC%2FeX3X9RDaUZa9R92NiY%3D&reserved=0
> Since the SMBA and BMEC features have never appeared in /proc/cpuinfo there cannot
> be a user space that expects these flags in /proc/cpuinfo and thus no risk of
> breaking user space. User space can get information about SMBA and BMEC
> from the info directory.
ok. Got it.
>
> Later that thread discussed removal of existing resctrl feature flags from
> /proc/cpuinfo - that is what I think we shouldn't do since there are
> user space consumers of those flags. I thus agree that the task described in
> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Flkml%2FMW3PR12MB455384130AF0BDE3AF88BCF095FE9%40MW3PR12MB4553.namprd12.prod.outlook.com%2F&data=05%7C01%7CBabu.Moger%40amd.com%7C900eb41c0e6049dd342208daf4270d2b%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638090745842366944%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=kE7d0cFYyJq1n4ZKKeeF%2FC%2FFDDJy0Sc%2Fd5MZ%2Bc56WQw%3D&reserved=0
> can be dropped.
Sure.
> I do not think this is a big change ... just add the empty quotes to the
> two cpufeatures.h patches and a new snippet to the resctrl documentation.
How about this? I want to get this right.. Hopefully next version can be
final.
diff --git a/Documentation/x86/resctrl.rst b/Documentation/x86/resctrl.rst
index 2860856f4463..7df5889237f4 100644
--- a/Documentation/x86/resctrl.rst
+++ b/Documentation/x86/resctrl.rst
@@ -24,10 +24,15 @@ CDP (Code and Data Prioritization) "cdp_l3", "cdp_l2"
CQM (Cache QoS Monitoring) "cqm_llc", "cqm_occup_llc"
MBM (Memory Bandwidth Monitoring) "cqm_mbm_total",
"cqm_mbm_local"
MBA (Memory Bandwidth Allocation) "mba"
-SMBA (Slow Memory Bandwidth Allocation) "smba"
-BMEC (Bandwidth Monitoring Event Configuration) "bmec"
+SMBA (Slow Memory Bandwidth Allocation) ""
+BMEC (Bandwidth Monitoring Event Configuration) ""
===============================================
================================
+Historically, new features were made visible by default in
/proc/cpuinfo. This
+resulted in the feature flags becoming hard to parse by the humans.
Adding a new
+flag to /proc/cpuinfo should be avoided if user space can obtain
information
+about the feature from resctrl's info directory.
+
To use the feature mount the file system::
# mount -t resctrl resctrl [-o cdp[,cdpl2][,mba_MBps]] /sys/fs/resctrl
thanks
Babu
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