[RFC][PATCH] sched: fix GENTLE_FAIR_SLEEPERS dependency

Suresh Jayaraman
2009-12-04T09:29:20Z

The newly introduced GENTLE_FAIR_SLEEPERS does not seem to have any
effect without FAIR_SLEEPERS. Fix sysctl.sched_features to reflect
this. Without this change, a user who sets GENTLE_FAIR_SLEEPERS
without FAIR_SLEEPERS would assume gentle sleeper fairness which
is not guaranteed.

Signed-off-by: Suresh Jayaraman <sjayaraman@suse.de>
---

Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -761,10 +761,22 @@ sched_feat_write(struct file *filp, cons
int len = strlen(sched_feat_names[i]);

if (strncmp(cmp, sched_feat_names[i], len) == 0) {
- if (neg)
+ if (neg) {
sysctl_sched_features &= ~(1UL << i);
- else
+ /*
+ * GENTLE_FAIR_SLEEPERS have no effect without
+ * FAIR_SLEEPERS.
+ */
+ if (strncmp(cmp, "FAIR_SLEEPERS",
+ strlen("FAIR_SLEEPERS")) == 0)
+ sysctl_sched_features &= ~(1UL << i+1);
+ } else {
sysctl_sched_features |= (1UL << i);
+ if (strncmp(cmp, "GENTLE_FAIR_SLEEPERS",
+ strlen("GENTLE_FAIR_SLEEPERS"))
+ == 0)
+ sysctl_sched_features |= (1UL << i-1);
+ }
break;
}
}