linux-kernel - [PATCH] sched/topology: Don't set SD_BALANCE

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <20191014164408.32596-1-valentin.schneider@arm.com>
Date:   Mon, 14 Oct 2019 17:44:08 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...nel.org, peterz@...radead.org, vincent.guittot@...aro.org,
        juri.lelli@...hat.com, Dietmar.Eggemann@....com,
        morten.rasmussen@....com, seto.hidetoshi@...fujitsu.com,
        qperret@...gle.com
Subject: [PATCH] sched/topology: Don't set SD_BALANCE_WAKE on cpuset domain relax

As pointed out in commit

  182a85f8a119 ("sched: Disable wakeup balancing")

SD_BALANCE_WAKE is a tad too aggressive, and is usually left unset.

However, it turns out cpuset domain relaxation will unconditionally set it
on domains below the relaxation level. This made sense back when
SD_BALANCE_WAKE was set unconditionally, but it no longer is the case.

We can improve things slightly by noticing that set_domain_attribute() is
always called after sd_init(), so rather than setting flags we can rely on
whatever sd_init() is doing and only clear certain flags when above the
relaxation level.

While at it, slightly clean up the function and flip the relax level
check to be more human readable.

Signed-off-by: Valentin Schneider <valentin.schneider@....com>
---
I was tempted to put a

Fixes: 182a85f8a119 ("sched: Disable wakeup balancing")

but the SD setup code back then was a mess of SD_INIT() macros which I'm
not familiar with. It *looks* like the sequence was roughly the same as it
is now (i.e. set up domain flags, *then* call set_domain_attribute()) but
I'm not completely sure.
---
 kernel/sched/topology.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index b5667a273bf6..3623ffe85d18 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -1201,17 +1201,13 @@ static void set_domain_attribute(struct sched_domain *sd,
 	if (!attr || attr->relax_domain_level < 0) {
 		if (default_relax_domain_level < 0)
 			return;
-		else
-			request = default_relax_domain_level;
+		request = default_relax_domain_level;
 	} else
 		request = attr->relax_domain_level;
-	if (request < sd->level) {
+
+	if (sd->level > request) {
 		/* Turn off idle balance on this domain: */
 		sd->flags &= ~(SD_BALANCE_WAKE|SD_BALANCE_NEWIDLE);
-	} else {
-		/* Turn on idle balance on this domain: */
-		sd->flags |= (SD_BALANCE_WAKE|SD_BALANCE_NEWIDLE);
 	}
 }
 
--
2.22.0