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| author | Ben Horgan <ben.horgan@arm.com> | 2026-05-06 09:28:55 +0100 |
|---|---|---|
| committer | Borislav Petkov (AMD) <bp@alien8.de> | 2026-05-08 12:27:00 +0200 |
| commit | 1cfa74c683ea82d37156ccd7ab4f4659056dc701 (patch) | |
| tree | e845ebf839ef47e4a27461051ef53dda2f8e6b5c | |
| parent | 9a1646211f8c67c7c98f8109607e3b962aea13eb (diff) | |
fs/resctrl: Document tasks file behaviour for task id 0 and idle tasks
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 <ben.horgan@arm.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Babu Moger <babu.moger@amd.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Tested-by: Babu Moger <babu.moger@amd.com>
Link: https://lore.kernel.org/20260506082855.3694761-1-ben.horgan@arm.com
| -rw-r--r-- | Documentation/filesystems/resctrl.rst | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst index b388e9193896..e4b66af55ffb 100644 --- a/Documentation/filesystems/resctrl.rst +++ b/Documentation/filesystems/resctrl.rst @@ -575,6 +575,11 @@ All groups contain the following files: then the task must already belong to the CTRL_MON parent of this group. The task is removed from any previous MON group. + When writing to this file, a task id of 0 is interpreted as the + task id of the currently running task. On reading the file, a task + id of 0 will never be shown and there is no representation of the + idle tasks. Instead, a CPU's idle task is always considered as a + member of the group owning the CPU. "cpus": Reading this file shows a bitmask of the logical CPUs owned by |