linux-kernel - [PATCH] sched: Add CONFIG_SCHED

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Message-ID: <YKyhtwhEgvtUDOyl@hirez.programming.kicks-ass.net>
Date:   Tue, 25 May 2021 09:05:27 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Hugh Dickins <hughd@...gle.com>
Cc:     linux-kernel@...r.kernel.org, rdunlap@...radead.org,
        joel@...lfernandes.org, Ingo Molnar <mingo@...nel.org>,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com,
        Valentin Schneider <valentin.schneider@....com>
Subject: [PATCH] sched: Add CONFIG_SCHED_CORE help text

Subject: sched: Add CONFIG_SCHED_CORE help text
From: Peter Zijlstra <peterz@...radead.org>
Date: Tue May 25 08:53:28 CEST 2021

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

Requested-by: Hugh Dickins <hughd@...gle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/Kconfig.preempt |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

--- 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.
+