On Wed, Jun 07, 2017 at 08:42:24AM +0900, Byungchul Park wrote:
> On Tue, Jun 06, 2017 at 04:12:25PM +0100, Juri Lelli wrote:
> > Hi,
> >
> > On 02/06/17 16:31, Byungchul Park wrote:
> > > When the heap tree is empty, cp->elements[0].cpu has meaningless value.
>
> Hi,
>
> The meaningless value is 0.
>
> > > We need to consider the case.
> > >
> > > Signed-off-by: Byungchul Park <byungchul.p...@lge.com>
> > > ---
> > > kernel/sched/cpudeadline.c | 3 ++-
> > > 1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
> > > index d4a6963..9b314a9 100644
> > > --- a/kernel/sched/cpudeadline.c
> > > +++ b/kernel/sched/cpudeadline.c
> > > @@ -110,7 +110,8 @@ static void cpudl_heapify(struct cpudl *cp, int idx)
> > >
> > > static inline int cpudl_maximum_cpu(struct cpudl *cp)
> > > {
> > > - return cp->elements[0].cpu;
> > > + int cpu = cp->elements[0].cpu;
> > > + return cp->elements[cpu].idx == IDX_INVALID ? -1 : cpu;
> >
> > Mmm, don't we get a WARN from cpumask_check() if we return -1 here?
>
> The function does not return -1 without my patch.
>
> Right?
Or the following patch would be needed, instead.
----->8-----
>From cada1345bf0ff8e6b5743999509d2abcacd79a9e Mon Sep 17 00:00:00 2001
From: Byungchul Park <byungchul.p...@lge.com>
Date: Wed, 7 Jun 2017 09:05:34 +0900
Subject: [PATCH 2/2] sched/deadline: Initialize cp->elements[].cpu to an
invalid value
Currently, when the heap tree is empty, cpudl_maximum_cpu() returns 0,
which causes unnecessary migration. It has to return an invalid value
e.g. -1 to prevent that.
Signed-off-by: Byungchul Park <byungchul.p...@lge.com>
---
kernel/sched/cpudeadline.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
index d4a6963..0f67cea 100644
--- a/kernel/sched/cpudeadline.c
+++ b/kernel/sched/cpudeadline.c
@@ -266,8 +266,10 @@ int cpudl_init(struct cpudl *cp)
return -ENOMEM;
}
- for_each_possible_cpu(i)
+ for_each_possible_cpu(i) {
+ cp->elements[i].cpu = -1;
cp->elements[i].idx = IDX_INVALID;
+ }
return 0;
}
--
1.9.1
