linux-kernel - [tip:sched/core] sched/core: Clarify SD

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Message-ID: <tip-94f438c84e850570f28dd36588a0d7f73b991e44@git.kernel.org>
Date:	Thu, 18 Aug 2016 03:56:06 -0700
From:	tip-bot for Peter Zijlstra <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org, tglx@...utronix.de,
	torvalds@...ux-foundation.org, peterz@...radead.org, efault@....de,
	hpa@...or.com, morten.rasmussen@....com
Subject: [tip:sched/core] sched/core: Clarify SD_flags comment

Commit-ID:  94f438c84e850570f28dd36588a0d7f73b991e44
Gitweb:     http://git.kernel.org/tip/94f438c84e850570f28dd36588a0d7f73b991e44
Author:     Peter Zijlstra <peterz@...radead.org>
AuthorDate: Mon, 15 Aug 2016 12:54:59 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Thu, 18 Aug 2016 11:26:52 +0200

sched/core: Clarify SD_flags comment

The SD_flags comment is very terse and doesn't explain why PACKING is
odd.

IIRC the distinction is that the 'normal' ones only describe topology,
while the ASYM_PACKING one also prescribes behaviour. It is odd in the
way that it doesn't only describe things.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mike Galbraith <efault@....de>
Cc: Morten Rasmussen <morten.rasmussen@....com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: dietmar.eggemann@....com
Cc: freedom.tan@...iatek.com
Cc: keita.kobayashi.ym@...esas.com
Cc: mgalbraith@...e.de
Cc: sgurrappadi@...dia.com
Cc: vincent.guittot@...aro.org
Cc: yuyang.du@...el.com
Link: http://lkml.kernel.org/r/20160815105459.GS6879@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/sched/core.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3b6b23c..54fff81 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6355,13 +6355,19 @@ static int sched_domains_curr_level;
 /*
  * SD_flags allowed in topology descriptions.
  *
- * SD_SHARE_CPUCAPACITY      - describes SMT topologies
- * SD_SHARE_PKG_RESOURCES - describes shared caches
- * SD_NUMA                - describes NUMA topologies
- * SD_SHARE_POWERDOMAIN   - describes shared power domain
+ * These flags are purely descriptive of the topology and do not prescribe
+ * behaviour. Behaviour is artificial and mapped in the below sd_init()
+ * function:
  *
- * Odd one out:
- * SD_ASYM_PACKING        - describes SMT quirks
+ *   SD_SHARE_CPUCAPACITY   - describes SMT topologies
+ *   SD_SHARE_PKG_RESOURCES - describes shared caches
+ *   SD_NUMA                - describes NUMA topologies
+ *   SD_SHARE_POWERDOMAIN   - describes shared power domain
+ *
+ * Odd one out, which beside describing the topology has a quirk also
+ * prescribes the desired behaviour that goes along with it:
+ *
+ *   SD_ASYM_PACKING        - describes SMT quirks
  */
 #define TOPOLOGY_SD_FLAGS		\
 	(SD_SHARE_CPUCAPACITY |		\