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b=k3q+X2tmP+EXftIZHYw7MsFwvU4wA0UOr6IVXVQnJ1dBsxYdEIPVOlW4yfA9Mrhckc59zRyQK8cEzo9UlgbvlfJINYhjMgq8CKd9kokeTxugIiZLw/ONcpTwPtxYO/ymJ+X0JlnwPfOI/gvd+ivP6Hg4Q3BgL2EcX3HmYy3jlvc= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from IA0PPF9A76BB3A6.namprd12.prod.outlook.com (2603:10b6:20f:fc04::bdc) by SA0PR12MB4383.namprd12.prod.outlook.com (2603:10b6:806:94::12) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8964.25; Fri, 8 Aug 2025 21:10:52 +0000 Received: from IA0PPF9A76BB3A6.namprd12.prod.outlook.com ([fe80::bed0:97a3:545d:af16]) by IA0PPF9A76BB3A6.namprd12.prod.outlook.com ([fe80::bed0:97a3:545d:af16%7]) with mapi id 15.20.8989.011; Fri, 8 Aug 2025 21:10:51 +0000 Message-ID: <35369f95-ef31-47fc-bb8d-c64e1b9f4748@amd.com> Date: Fri, 8 Aug 2025 16:10:46 -0500 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v16 27/34] fs/resctrl: Introduce mbm_assign_on_mkdir to enable assignments on mkdir To: Reinette Chatre , corbet@lwn.net, tony.luck@intel.com, james.morse@arm.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com Cc: Dave.Martin@arm.com, x86@kernel.org, hpa@zytor.com, akpm@linux-foundation.org, paulmck@kernel.org, rostedt@goodmis.org, Neeraj.Upadhyay@amd.com, david@redhat.com, arnd@arndb.de, fvdl@google.com, seanjc@google.com, jpoimboe@kernel.org, pawan.kumar.gupta@linux.intel.com, xin@zytor.com, manali.shukla@amd.com, tao1.su@linux.intel.com, sohil.mehta@intel.com, kai.huang@intel.com, xiaoyao.li@intel.com, peterz@infradead.org, xin3.li@intel.com, kan.liang@linux.intel.com, mario.limonciello@amd.com, thomas.lendacky@amd.com, perry.yuan@amd.com, gautham.shenoy@amd.com, chang.seok.bae@intel.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, peternewman@google.com, eranian@google.com References: Content-Language: en-US From: "Moger, Babu" In-Reply-To: Content-Type: text/plain; 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On 8/8/2025 4:00 PM, Reinette Chatre wrote: > Hi Babu, > > On 8/8/25 1:29 PM, Moger, Babu wrote: >> Hi Reinette, >> >> On 7/30/2025 3:08 PM, Reinette Chatre wrote: >>> Hi Babu, >>> >>> On 7/25/25 11:29 AM, Babu Moger wrote: >>>> The "mbm_event" counter assignment mode allows users to assign a hardware >>>> counter to an RMID, event pair and monitor the bandwidth as long as it is >>>> assigned. >>> Above implies this addition is in support of "mbm_event" mode while the >>> implementation applies to any and all assignable counter modes, including >>> the "default" and for example the upcoming "soft-ABMC". It is clear to me >>> how this is used and interpreted when "mbm_event" mode is enabled, but not >>> for the others (more below). >>> >>>> Introduce a user-configurable option that determines if a counter will >>>> automatically be assigned to an RMID, event pair when its associated >>>> monitor group is created via mkdir. >>>> >>>> Suggested-by: Peter Newman >>>> Signed-off-by: Babu Moger >>>> --- >>> ... >>> >>>> --- >>>>   Documentation/filesystems/resctrl.rst | 16 ++++++++++ >>>>   fs/resctrl/monitor.c                  |  2 ++ >>>>   fs/resctrl/rdtgroup.c                 | 43 +++++++++++++++++++++++++++ >>>>   include/linux/resctrl.h               |  3 ++ >>>>   4 files changed, 64 insertions(+) >>>> >>>> diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst >>>> index 37dbad4d50f7..165e0d315af7 100644 >>>> --- a/Documentation/filesystems/resctrl.rst >>>> +++ b/Documentation/filesystems/resctrl.rst >>>> @@ -354,6 +354,22 @@ with the following files: >>>>         # cat /sys/fs/resctrl/info/L3_MON/event_configs/mbm_total_bytes/event_filter >>>>          local_reads,local_non_temporal_writes >>>>   +"mbm_assign_on_mkdir": >>> Needs a "Exists when "mbm_event" counter assignment mode is supported."? >>> Also needs clarification on on behavior when "mbm_event" is enabled vs. disabled. >> I think we should allow it to modify  only when "mbm_event" is enabled. >>>> +    Determines if a counter will automatically be assigned to an RMID, event pair >>> "will automatically be" -> "is automatically" >>> "RMID, event" -> "RMID, MBM event" >> Sure. >>>> +    when its associated monitor group is created via mkdir. It is enabled by default >>>> +    on boot and users can disable by writing to the interface. >>> "users can disable" -> "users can disable this capability" or "can be disabled"? >> Sure. >>> This implementation enables user to read/write this file/property when "mbm_event" mode is >>> disabled. Considering this explanation I do not think it is clear how this file reflects >>> system behavior when in "default" mode. There is no difference between mbm_assign_on_mkdir >>> enabled/disabled when in "default" mode, no? >> Yes. So, we should only allow modifications only when mbm_event mode is enabled. >>> Should interactions with "mbm_assign_on_mkdir" be restricted to when >>> "mbm_event" mode is enabled? If so, the next question would likely be whether value >> Yes. >>> should change during "mbm_event" enable->disable or "disable->enable". Above states >>> clearly that it is enabled on boot and it may be reasonable to have it keep (but not always >>> expose) user's setting when switching between modes. >>> >>> Restricting it to "mbm_event" mode now gives us some flexibility when soft-ABMC follows >>> on if/how it can/should support this. What do you think? >> Yes. We should restrict it to modify only when mbm_event mode is enabled. > I agree. I also think it should not be displayed with mbm_event mode is disabled. This is > because it indicates to user space that counters are automatically assigned to RMID, event > pairs and since "default" mode depends on hardware doing this it may not be accurate when, for > example, ABMC is disabled. Alternative is to add a third value, for example "enabled", "disabled", and > "undefined"(?). This sounds a bit awkward though so I think simplest may be to have this file > also be consistent with the others and return error when mbm_event mode is disabled. Yes. We can do that. > >> And always enable it when switching from >> >> "mbm_event" disable -> enable:  r->mon.mbm_assign_on_mkdir = true; >> >> "mbm_event" enable -> enable: "no need to modify as the value does not affect the behavior." >> > ok, please note this may need an update to the doc that currently only states "enabled by > default on boot" to indicate it is also automatically enabled when enabling mbm_event mode. Will add texts about it. Thanks Babu