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Message-ID: <102328ce-39fe-44a0-884a-1ba74c4bbaef@amd.com> Date: Wed, 25 Jun 2025 15:14:41 -0500 From: "Moger, Babu" <babu.moger@....com> To: Reinette Chatre <reinette.chatre@...el.com>, corbet@....net, tony.luck@...el.com, Dave.Martin@....com, james.morse@....com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com Cc: x86@...nel.org, hpa@...or.com, akpm@...ux-foundation.org, rostedt@...dmis.org, paulmck@...nel.org, thuth@...hat.com, ardb@...nel.org, gregkh@...uxfoundation.org, seanjc@...gle.com, thomas.lendacky@....com, pawan.kumar.gupta@...ux.intel.com, manali.shukla@....com, perry.yuan@....com, kai.huang@...el.com, peterz@...radead.org, xiaoyao.li@...el.com, kan.liang@...ux.intel.com, mario.limonciello@....com, xin3.li@...el.com, gautham.shenoy@....com, xin@...or.com, chang.seok.bae@...el.com, fenghuay@...dia.com, peternewman@...gle.com, maciej.wieczor-retman@...el.com, eranian@...gle.com, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH v14 11/32] fs/resctrl: Introduce the interface to display monitoring modes Hi Reinette, On 6/24/25 17:47, Reinette Chatre wrote: > Hi Babu, > > On 6/13/25 2:04 PM, Babu Moger wrote: >> Introduce the resctrl file "mbm_assign_mode" to list the supported >> monitoring modes. > > "the supported monitoring modes" -> "the supported counter assignment modes"? Sure. > >> >> The "mbm_event" mode allows users to assign a hardware counter ID to an > > nit: users do not assign/pick the ID, this is done by resctrl. So perhaps > just "users to assign a hardware counter to ..." Sure. > >> RMID, event pair and monitor bandwidth usage as long as it is assigned. >> The hardware continues to track the assigned counter until it is >> explicitly unassigned by the user. Each event within a resctrl group >> can be assigned independently in this mode. >> >> On AMD systems "mbm_event" mode is backed by the ABMC (Assignable >> Bandwidth Monitoring Counters) hardware feature and is enabled by default. >> >> The "default" mode is the existing mode that works without the explicit >> counter assignment, instead relying on dynamic counter assignment by >> hardware that may result in hardware not dedicating a counter resulting >> in monitoring data reads returning "Unavailable". >> >> Provide an interface to display the monitor modes on the system. >> >> $ cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode >> [mbm_event] >> default >> >> Add IS_ENABLED(CONFIG_RESCTRL_ASSIGN_FIXED) check to support Arm64. >> >> On x86, CONFIG_RESCTRL_ASSIGN_FIXED is not defined. On Arm64, it will be >> defined when the "mbm_event" mode is supported. >> >> Add IS_ENABLED(CONFIG_RESCTRL_ASSIGN_FIXED) check early to ensure the user >> interface remains compatible with upcoming Arm64 support. IS_ENABLED() >> safely evaluates to 0 when the configuration is not defined. >> >> As a result, for MPAM, the display would be either: >> [default] >> or >> [mbm_event] >> >> Signed-off-by: Babu Moger <babu.moger@....com> >> --- > > ... > >> --- >> Documentation/filesystems/resctrl.rst | 31 ++++++++++++++++++++++ >> fs/resctrl/rdtgroup.c | 37 +++++++++++++++++++++++++++ >> 2 files changed, 68 insertions(+) >> >> diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst >> index c97fd77a107d..4e76e4ac5d3a 100644 >> --- a/Documentation/filesystems/resctrl.rst >> +++ b/Documentation/filesystems/resctrl.rst >> @@ -257,6 +257,37 @@ with the following files: >> # cat /sys/fs/resctrl/info/L3_MON/mbm_local_bytes_config >> 0=0x30;1=0x30;3=0x15;4=0x15 >> >> +"mbm_assign_mode": >> + The supported monitoring modes. The enclosed brackets indicate which mode > > "The supported monitoring modes." -> "The supported counter assignment modes."? > Sure. >> + is enabled. >> + :: >> + >> + # cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode >> + [mbm_event] >> + default >> + >> + "mbm_event": >> + >> + mbm_event mode allows users to assign a hardware counter ID to an RMID, event > > "hardware counter ID" -> "hardware counter" > Sure. >> + pair and monitor the bandwidth usage as long as it is assigned. The hardware >> + continues to track the assigned counter until it is explicitly unassigned by >> + the user. Each event within a resctrl group can be assigned independently. >> + >> + In this mode, a monitoring event can only accumulate data while it is backed >> + by a hardware counter. Use "mbm_L3_assignments" found in each CTRL_MON and MON >> + group to specify which of the events should have a counter assigned. The number >> + of counters available is described in the "num_mbm_cntrs" file. Changing the >> + mode may cause all counters on the resource to reset. >> + >> + "default": >> + >> + In default mode, resctrl assumes there is a hardware counter for each >> + event within every CTRL_MON and MON group. On AMD platforms, it is >> + recommended to use the mbm_event mode, if supported, to prevent reset of MBM >> + events between reads resulting from hardware re-allocating counters. This can >> + result in misleading values or display "Unavailable" if no counter is assigned >> + to the event. >> + >> "max_threshold_occupancy": >> Read/write file provides the largest value (in >> bytes) at which a previously used LLC_occupancy > > Reinette > > -- Thanks Babu Moger
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