| Message ID | 1464001138-25063-5-git-send-email-morten.rasmussen@arm.com |
|---|---|
| State | Superseded |
| Headers | show |
On Tue, May 24, 2016 at 08:29:05AM +0200, Mike Galbraith wrote: > On Mon, 2016-05-23 at 11:58 +0100, Morten Rasmussen wrote: > > In the current find_idlest_group()/find_idlest_cpu() search we end up > > calling find_idlest_cpu() in a sched_group containing only one cpu in > > the end. Checking idle-states becomes pointless when there is no > > alternative, so bail out instead. > > > > cc: Ingo Molnar <mingo@redhat.com> > > cc: Peter Zijlstra <peterz@infradead.org> > > > > Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com> > > --- > > kernel/sched/fair.c | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > index 0fe3020..564215d 100644 > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -5155,6 +5155,11 @@ find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu) > > > > int shallowest_idle_cpu = -1; > > > > int i; > > > > +> > /* Check if we have any choice */ > > +> > if (group->group_weight == 1) { > > +> > > return cpumask_first(sched_group_cpus(group)); > > +> > } > > + > > Hm, if task isn't allowed there, too bad? Is that possible for single-cpu groups? I thought we skipped groups with no cpus allowed in find_idlest_group(): /* Skip over this group if it has no CPUs allowed */ if (!cpumask_intersects(sched_group_cpus(group), tsk_cpus_allowed(p))) continue; Since the group has at least one cpu allowed and only contains one cpu, that cpu must be allowed. No?
On Wed, Jun 01, 2016 at 09:59:20PM +0200, Peter Zijlstra wrote: > On Mon, May 23, 2016 at 11:58:46AM +0100, Morten Rasmussen wrote: > > In the current find_idlest_group()/find_idlest_cpu() search we end up > > calling find_idlest_cpu() in a sched_group containing only one cpu in > > the end. Checking idle-states becomes pointless when there is no > > alternative, so bail out instead. > > > > cc: Ingo Molnar <mingo@redhat.com> > > cc: Peter Zijlstra <peterz@infradead.org> > > > > Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com> > > --- > > kernel/sched/fair.c | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > index 0fe3020..564215d 100644 > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -5155,6 +5155,11 @@ find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu) > > int shallowest_idle_cpu = -1; > > int i; > > > > + /* Check if we have any choice */ > > + if (group->group_weight == 1) { > > + return cpumask_first(sched_group_cpus(group)); > > + } > > superfluous brackets, also isn't @this_cpu supposed to be part of the > sched_group_cpu(group) mask? I'll kill the brackets. IIUC, @this_cpu is never part of sched_group_cpus(group). find_idlest_group() never returns the local group, so if we manage to get to find_idlest_cpu(), the group would not contain @this_cpu.
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 0fe3020..564215d 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5155,6 +5155,11 @@ find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu) int shallowest_idle_cpu = -1; int i; + /* Check if we have any choice */ + if (group->group_weight == 1) { + return cpumask_first(sched_group_cpus(group)); + } + /* Traverse only the allowed CPUs */ for_each_cpu_and(i, sched_group_cpus(group), tsk_cpus_allowed(p)) { if (idle_cpu(i)) {
In the current find_idlest_group()/find_idlest_cpu() search we end up calling find_idlest_cpu() in a sched_group containing only one cpu in the end. Checking idle-states becomes pointless when there is no alternative, so bail out instead. cc: Ingo Molnar <mingo@redhat.com> cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com> --- kernel/sched/fair.c | 5 +++++ 1 file changed, 5 insertions(+) -- 1.9.1