[tip: sched/core] sched: Add CONFIG_SCHED_CORE help text

[tip-bot2 for Peter Zijlstra]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     7b419f47facd286c6723daca6ad69ec355473f78
Gitweb:        https://git.kernel.org/tip/7b419f47facd286c6723daca6ad69ec355473f78
Author:        Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate:    Tue, 25 May 2021 08:53:28 +02:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Tue, 01 Jun 2021 16:00:10 +02:00

sched: Add CONFIG_SCHED_CORE help text

Hugh noted that the SCHED_CORE Kconfig option could do with a help
text.

Requested-by: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/YKyhtwhEgvtUDOyl@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
---
 kernel/Kconfig.preempt | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
index ea1e333..bd7c414 100644
--- a/kernel/Kconfig.preempt
+++ b/kernel/Kconfig.preempt
@@ -104,4 +104,18 @@ config SCHED_CORE
 	bool "Core Scheduling for SMT"
 	default y
 	depends on SCHED_SMT
+	help
+	  This option permits Core Scheduling, a means of coordinated task
+	  selection across SMT siblings. When enabled -- see
+	  prctl(PR_SCHED_CORE) -- task selection ensures that all SMT siblings
+	  will execute a task from the same 'core group', forcing idle when no
+	  matching task is found.
+
+	  Use of this feature includes:
+	   - mitigation of some (not all) SMT side channels;
+	   - limiting SMT interference to improve determinism and/or performance.
+
+	  SCHED_CORE is default enabled when SCHED_SMT is enabled -- when
+	  unused there should be no impact on performance.
+