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Message-ID: <MW3PR12MB45534504C044EBAEABA9E9E295FD9@MW3PR12MB4553.namprd12.prod.outlook.com>
Date: Thu, 12 Jan 2023 00:47:46 +0000
From: "Moger, Babu" <Babu.Moger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>,
"corbet@....net" <corbet@....net>,
"tglx@...utronix.de" <tglx@...utronix.de>,
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Subject: RE: [PATCH v11 13/13] Documentation/x86: Update resctrl.rst for new
features
[AMD Official Use Only - General]
Hi Reinette,
> -----Original Message-----
> From: Reinette Chatre <reinette.chatre@...el.com>
> Sent: Wednesday, January 11, 2023 4:56 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 1/11/2023 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.kern
> el.org%2Flkml%2FY7xjxUj%2BKnOEJssZ%40zn.tnic%2F&data=05%7C01%7CBabu
> .Moger%40amd.com%7C900eb41c0e6049dd342208daf4270d2b%7C3dd8961fe
> 4884e608e11a82d994e183d%7C0%7C0%7C638090745842366944%7CUnknown
> %7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWw
> iLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=%2F5GVOhnxq1%2B3nJwGtlAp
> vLfC%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.
>
> 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.kern
> el.org%2Flkml%2FMW3PR12MB455384130AF0BDE3AF88BCF095FE9%40MW3P
> R12MB4553.namprd12.prod.outlook.com%2F&data=05%7C01%7CBabu.Moger
> %40amd.com%7C900eb41c0e6049dd342208daf4270d2b%7C3dd8961fe4884e6
> 08e11a82d994e183d%7C0%7C0%7C638090745842366944%7CUnknown%7CTW
> FpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVC
> I6Mn0%3D%7C3000%7C%7C%7C&sdata=kE7d0cFYyJq1n4ZKKeeF%2FC%2FFDDJ
> y0Sc%2Fd5MZ%2Bc56WQw%3D&reserved=0
> can be dropped.
>
> 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.
Previous one got garbled. Here is the correct one.
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
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