kernel/git/stable/linux.git/Documentation/filesystems/resctrl.rst, branch linux-7.2.y

fs/resctrl: Document tasks file behaviour for task id 0 and idle tasks

2026-05-08T10:27:00+00:00

When 0 is written to the tasks file it is interpreted as the current task in rdtgroup_move_task(). Each CPU's idle task has task_struct::pid set to 0 and, on x86, task_struct::closid to RESCTRL_RESERVED_CLOSID and task_struct::rmid to RESCTRL_RESERVED_RMID. Equivalently, on MPAM platforms, thread_info::mpam_partid_pmg is encoded with PARTID and PMG set to RESCTRL_RESERVED_CLOSID and RESCTRL_RESERVED_RMID, respectively. As there is no interface to change these from the default, the resctrl configuration for the idle tasks is fixed and they always behave equivalently to a task in the default tasks file and so take their configuration from the cpus/cpus_list files. On read of the tasks file, show_rdt_tasks() filters out any 0 PID. Hence, a task id of 0 is never shown in the tasks file and the idle tasks are not represented either. Document the user visible behaviour. Signed-off-by: Ben Horgan Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Babu Moger Reviewed-by: Reinette Chatre Tested-by: Babu Moger Link: https://lore.kernel.org/20260506082855.3694761-1-ben.horgan@arm.com

fs/resctrl: Document that automatic counter assignment is best effort

2026-05-08T10:25:22+00:00

When using automatic counter assignment it's useful for a user to know which counters they can expect to be assigned on group creation. Document that automatic counter assignment is best effort and how to discover any assignment failures. Suggested-by: Reinette Chatre Signed-off-by: Ben Horgan Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Babu Moger Reviewed-by: Reinette Chatre Tested-by: Babu Moger Link: https://lore.kernel.org/20260506082855.3694761-1-ben.horgan@arm.com

x86,fs/resctrl: Create 'event_filter' files read only if they're not configurable

2026-05-06T17:06:57+00:00

When the counter assignment mode is mbm_event resctrl assumes the MBM events are configurable and exposes the 'event_filter' files. These files live at info/L3_MON/event_configs//event_filter and are used to display and set the event configuration. The MPAM architecture has support for configuring the memory bandwidth utilization (MBWU) counters to only count reads or only count writes. However, in MPAM, this event filtering support is optional in the hardware (and not yet implemented in the MPAM driver) but MBM counter assignment is always possible for MPAM MBWU counters. In order to support mbm_event mode with MPAM, create the 'event_filter' files read only if the event configuration can't be changed. A user can still chmod the file and so also return early with an error from event_filter_write(). Introduce a new monitor property, mbm_cntr_configurable, to indicate whether or not assignable MBM counters are configurable. On x86, set this to true whenever mbm_cntr_assignable is true to keep existing behaviour. Signed-off-by: Ben Horgan Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Reinette Chatre Reviewed-by: Babu Moger Tested-by: Babu Moger Link: https://lore.kernel.org/20260506082855.3694761-1-ben.horgan@arm.com

fs/resctrl: Add "*" shorthand to set io_alloc CBM for all domains

2026-04-01T22:22:59+00:00

Configuring the io_alloc_cbm interface requires an explicit domain ID for each cache domain. On systems with high core counts and numerous cache clusters, this requirement becomes cumbersome for automation and management tasks that aim to apply a uniform policy. Introduce a wildcard domain ID selector "*" for the io_alloc_cbm interface. This enables users to set the same Capacity Bitmask (CBM) across all cache domains in a single operation. Signed-off-by: Aaron Tomlin Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Reinette Chatre Reviewed-by: Babu Moger Tested-by: Babu Moger Link: https://patch.msgid.link/20260325001159.447075-3-atomlin@atomlin.com

Merge tag 'x86_cache_for_v7.0_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2026-02-11T02:24:56+00:00

Pull x86 resource control updates from Borislav Petkov: - Extend the resctrl machinery to support telemetry monitoring on Intel (Tony Luck) The practical usage of this is being able to tell how much energy or how much work can be attributed to a group of tasks tracked under a single idenitifier. Prepend this work with proper refactoring of resctrl domains handling code. * tag 'x86_cache_for_v7.0_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (30 commits) x86,fs/resctrl: Update documentation for telemetry events x86/resctrl: Enable RDT_RESOURCE_PERF_PKG fs/resctrl: Move RMID initialization to first mount x86,fs/resctrl: Compute number of RMIDs as minimum across resources fs/resctrl: Move allocation/free of closid_num_dirty_rmid[] x86/resctrl: Handle number of RMIDs supported by RDT_RESOURCE_PERF_PKG x86/resctrl: Add energy/perf choices to rdt boot option x86,fs/resctrl: Handle domain creation/deletion for RDT_RESOURCE_PERF_PKG fs/resctrl: Refactor rmdir_mondata_subdir_allrdtgrp() fs/resctrl: Refactor mkdir_mondata_subdir() x86/resctrl: Read telemetry events x86/resctrl: Find and enable usable telemetry events x86,fs/resctrl: Add architectural event pointer x86,fs/resctrl: Fill in details of events for performance and energy GUIDs x86/resctrl: Discover hardware telemetry events fs/resctrl: Emphasize that L3 monitoring resource is required for summing domains x86,fs/resctrl: Add and initialize a resource for package scope monitoring x86,fs/resctrl: Add an architectural hook called for first mount x86,fs/resctrl: Support binary fixed point event counters x86,fs/resctrl: Handle events that can be read from any CPU ...

docs: fix 're-use' -> 'reuse' in documentation

2026-02-02T16:54:15+00:00

Signed-off-by: Rhys Tumelty Acked-by: Randy Dunlap Signed-off-by: Jonathan Corbet Message-ID: <20260128220233.179439-1-rhys@tumelty.co.uk>

x86,fs/resctrl: Update documentation for telemetry events

2026-01-10T19:25:51+00:00

Update resctrl filesystem documentation with the details about the resctrl files that support telemetry events. [ bp: Drop the debugfs hunk of the documentation until a better debugging solution is found. ] Signed-off-by: Tony Luck Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Reinette Chatre Link: https://lore.kernel.org/20251217172121.12030-1-tony.luck@intel.com

fs/resctrl: Update bit_usage to reflect io_alloc

2025-11-22T13:30:34+00:00

The "shareable_bits" and "bit_usage" resctrl files associated with cache resources give insight into how instances of a cache is used. Update the annotated capacity bitmasks displayed by "bit_usage" to include the cache portions allocated for I/O via the "io_alloc" feature. "shareable_bits" is a global bitmask of shareable cache with I/O and can thus not present the per-domain I/O allocations possible with the "io_alloc" feature. Revise the "shareable_bits" documentation to direct users to "bit_usage" for accurate cache usage information. Signed-off-by: Babu Moger Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Reinette Chatre Link: https://patch.msgid.link/e02a0d424129fd7f3e45822a559b1c614ae4652a.1762995456.git.babu.moger@amd.com

fs/resctrl: Introduce interface to modify io_alloc capacity bitmasks

2025-11-22T13:28:31+00:00

The io_alloc feature in resctrl enables system software to configure the portion of the cache allocated for I/O traffic. When supported, the io_alloc_cbm file in resctrl provides access to capacity bitmasks (CBMs) allocated for I/O devices. Enable users to modify io_alloc CBMs by writing to the io_alloc_cbm resctrl file when the io_alloc feature is enabled. Mirror the CBMs between CDP_CODE and CDP_DATA when CDP is enabled to present consistent I/O allocation information to user space. Signed-off-by: Babu Moger Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Reinette Chatre Link: https://patch.msgid.link/67609641b03ccfba18a8ee0bf9dbd1f3dcbecda3.1762995456.git.babu.moger@amd.com

fs/resctrl: Introduce interface to display io_alloc CBMs

2025-11-22T10:37:21+00:00

Introduce the "io_alloc_cbm" resctrl file to display the capacity bitmasks (CBMs) that represent the portions of each cache instance allocated for I/O traffic on a cache resource that supports the "io_alloc" feature. io_alloc_cbm resides in the info directory of a cache resource, for example, /sys/fs/resctrl/info/L3/. Since the resource name is part of the path, it is not necessary to display the resource name as done in the schemata file. When CDP is enabled, io_alloc routes traffic using the highest CLOSID associated with the CDP_CODE resource and that CLOSID becomes unusable for the CDP_DATA resource. The highest CLOSID of CDP_CODE and CDP_DATA resources will be kept in sync to ensure consistent user interface. In preparation for this, access the CBMs for I/O traffic through highest CLOSID of either CDP_CODE or CDP_DATA resource. Signed-off-by: Babu Moger Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Reinette Chatre Link: https://patch.msgid.link/55a3ff66a70e7ce8239f022e62b334e9d64af604.1762995456.git.babu.moger@amd.com