Documentation: intel_pstate: Fix description of asymmetric packing with SMT

Patchset [1], including commits

 046a5a95c3b0 ("x86/sched/itmt: Give all SMT siblings of a core the same priority")
 995998ebdebd ("x86/sched: Remove SD_ASYM_PACKING from the SMT domain flags")

overhauled asym_packing handling in the scheduler on x86 hybrid
processors with SMT. It removed SD_ASYM_PACKING from the x86 SMT
scheduling domain and made all SMT siblings of a core share the same
priority. As a result, asym_packing operates only across physical
cores, spreading tasks among them and only using idle SMT siblings
once all physical cores are busy.

Fix the documentation to reflect this behavior.

Fixes: f20af84c29b2 ("cpufreq: intel_pstate: Document hybrid processor support")
Link: https://lore.kernel.org/r/20230406203148.19182-1-ricardo.neri-calderon@linux.intel.com
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
[ rjw: Changelog edits ]
Link: https://patch.msgid.link/20260424-rneri-fix-intel-pstate-doc-smt-asym-packing-v1-1-317bf7d5c362@linux.intel.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/Documentation/admin-guide/pm/intel_pstate.rst b/Documentation/admin-guide/pm/intel_pstate.rst
index fde967b0c2e0e5c5b43d3b043fb3478025308722..25fe5d88fea6c73a2cdf2ea8462c167418476856 100644 (file)
--- a/Documentation/admin-guide/pm/intel_pstate.rst
+++ b/Documentation/admin-guide/pm/intel_pstate.rst
@@ -355,11 +355,12 @@ HyperThreading (HT) in the context of Intel processors, is enabled on at least
 one core, ``intel_pstate`` assigns performance-based priorities to CPUs.  Namely,
 the priority of a given CPU reflects its highest HWP performance level which
 causes the CPU scheduler to generally prefer more performant CPUs, so the less
-performant CPUs are used when the other ones are fully loaded.  However, SMT
-siblings (that is, logical CPUs sharing one physical core) are treated in a
-special way such that if one of them is in use, the effective priority of the
-other ones is lowered below the priorities of the CPUs located in the other
-physical cores.
+performant CPUs are used when the other ones are fully loaded.  SMT siblings
+(that is, logical CPUs sharing one physical core) are given the same priority.
+The scheduler can pull tasks from lower-priority cores and place them on any
+sibling.  Since the scheduler spreads tasks among physical cores, tasks will be
+placed on the SMT siblings of physical cores only after all physical cores are
+busy.
 
 This approach maximizes performance in the majority of cases, but unfortunately
 it also leads to excessive energy usage in some important scenarios, like video