linux-kernel - [PATCH v3 7/7] sched/topology: Use prebuilt SD flag degeneration mask

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Message-Id: <20200701190656.10126-8-valentin.schneider@arm.com>
Date:   Wed,  1 Jul 2020 20:06:55 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     linux-kernel@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>, mingo@...nel.org,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        morten.rasmussen@....com
Subject: [PATCH v3 7/7] sched/topology: Use prebuilt SD flag degeneration mask

Leverage SD_DEGENERATE_GROUPS_MASK in sd_degenerate() and
sd_degenerate_parent().

Note that this changes sd_degenerate() somewhat: I'm using the negation of
SD_DEGENERATE_GROUPS_MASK as the mask of flags not requiring groups, which
is equivalent to:

SD_WAKE_AFFINE | SD_SERIALIZE | SD_NUMA

whereas the current mask for that is simply

SD_WAKE_AFFINE

I played with a few toy NUMA topologies on QEMU and couldn't cause a
different degeneration than what mainline does currently. If that is deemed
too risky, we can go back to using SD_WAKE_AFFINE explicitly.

Suggested-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Valentin Schneider <valentin.schneider@....com>
---
 kernel/sched/topology.c | 24 +++---------------------
 1 file changed, 3 insertions(+), 21 deletions(-)

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index fe393b295444..a135a0c99b16 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -160,22 +160,13 @@ static int sd_degenerate(struct sched_domain *sd)
 		return 1;
 
 	/* Following flags need at least 2 groups */
-	if (sd->flags & (SD_BALANCE_NEWIDLE |
-			 SD_BALANCE_WAKE |
-			 SD_BALANCE_FORK |
-			 SD_BALANCE_EXEC |
-			 SD_ASYM_PACKING |
-			 SD_SHARE_CPUCAPACITY |
-			 SD_ASYM_CPUCAPACITY |
-			 SD_SHARE_PKG_RESOURCES |
-			 SD_OVERLAP |
-			 SD_PREFER_SIBLING)) {
+	if (sd->flags & SD_DEGENERATE_GROUPS_MASK) {
 		if (sd->groups != sd->groups->next)
 			return 0;
 	}
 
 	/* Following flags don't use groups */
-	if (sd->flags & (SD_WAKE_AFFINE))
+	if (sd->flags & ~SD_DEGENERATE_GROUPS_MASK)
 		return 0;
 
 	return 1;
@@ -194,16 +185,7 @@ sd_parent_degenerate(struct sched_domain *sd, struct sched_domain *parent)
 
 	/* Flags needing groups don't count if only 1 group in parent */
 	if (parent->groups == parent->groups->next) {
-		pflags &= ~(SD_BALANCE_NEWIDLE |
-			    SD_BALANCE_WAKE |
-			    SD_BALANCE_FORK |
-			    SD_BALANCE_EXEC |
-			    SD_ASYM_PACKING |
-			    SD_ASYM_CPUCAPACITY |
-			    SD_SHARE_CPUCAPACITY |
-			    SD_SHARE_PKG_RESOURCES |
-			    SD_OVERLAP |
-			    SD_PREFER_SIBLING);
+		pflags &= ~SD_DEGENERATE_GROUPS_MASK;
 		if (nr_node_ids == 1)
 			pflags &= ~SD_SERIALIZE;
 	}
-- 
2.27.0