linux-kernel - [PATCH v2] sched/fair: fix initial util

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]

Date: Thu, 14 Mar 2024 18:59:16 -0700
From: Dawei Li <daweilics@...il.com>
To: 
Cc: Dawei Li <daweilics@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	Valentin Schneider <vschneid@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2] sched/fair: fix initial util_avg calculation

Change se->load.weight to se_weight(se) in the calculation for the
initial util_avg to avoid unnecessarily inflating the util_avg by 1024
times.

The reason is that se->load.weight has the unit/scale as the scaled-up
load, while cfs_rg->avg.load_avg has the unit/scale as the true task
weight (as mapped directly from the task's nice/priority value). With
CONFIG_32BIT, the scaled-up load is equal to the true task weight. With
CONFIG_64BIT, the scaled-up load is 1024 times the true task weight.
Thus, the current code may inflate the util_avg by 1024 times. The
follow-up capping will not allow the util_avg value to go wild. But the
calculation should have the correct logic.

Signed-off-by: Dawei Li <daweilics@...il.com>
---
Changes in v2:
- update the commit message
---
 kernel/sched/fair.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a19ea290b790..5f98f639bdb9 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1031,7 +1031,8 @@ void init_entity_runnable_average(struct sched_entity *se)
  * With new tasks being created, their initial util_avgs are extrapolated
  * based on the cfs_rq's current util_avg:
  *
- *   util_avg = cfs_rq->util_avg / (cfs_rq->load_avg + 1) * se.load.weight
+ *   util_avg = cfs_rq->avg.util_avg / (cfs_rq->avg.load_avg + 1)
+ *		* se_weight(se)
  *
  * However, in many cases, the above util_avg does not give a desired
  * value. Moreover, the sum of the util_avgs may be divergent, such
@@ -1078,7 +1079,7 @@ void post_init_entity_util_avg(struct task_struct *p)
 
 	if (cap > 0) {
 		if (cfs_rq->avg.util_avg != 0) {
-			sa->util_avg  = cfs_rq->avg.util_avg * se->load.weight;
+			sa->util_avg  = cfs_rq->avg.util_avg * se_weight(se);
 			sa->util_avg /= (cfs_rq->avg.load_avg + 1);
 
 			if (sa->util_avg > cap)
-- 
2.40.1