Applies to 2.6.23-rc9-rt2... This is another RTO related fix from the thread
two days ago.
---
RT: Fix special-case exception for preempting the local CPU
Check whether the local CPU is eligible to take the task before trying to
preempt it.
Signed-off-by: Gregory Haskins <[email protected]>
---
kernel/sched.c | 3 ++-
1 files changed, 2 insertions(+), 1 deletions(-)
diff --git a/kernel/sched.c b/kernel/sched.c
index 3e75c62..b7f7a96 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1869,7 +1869,8 @@ out_activate:
* extra locking in this particular case, because
* we are on the current CPU.)
*/
- if (TASK_PREEMPTS_CURR(p, this_rq))
+ if (TASK_PREEMPTS_CURR(p, this_rq)
+ && cpu_isset(this_cpu, p->cpus_allowed))
set_tsk_need_resched(this_rq->curr);
else
/*
On Wed, Oct 10, 2007 at 10:49:35AM -0400, Gregory Haskins wrote:
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 3e75c62..b7f7a96 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -1869,7 +1869,8 @@ out_activate:
> * extra locking in this particular case, because
> * we are on the current CPU.)
> */
> - if (TASK_PREEMPTS_CURR(p, this_rq))
> + if (TASK_PREEMPTS_CURR(p, this_rq)
> + && cpu_isset(this_cpu, p->cpus_allowed))
> set_tsk_need_resched(this_rq->curr);
> else
> /*
I wonder if it might better to explicitly take the rq lock and try to
put the task on this_rq in this situation? Rather than waiting for
schedule to pull it from a remote rq as part of balance_rt_tasks.
A question that has passed through my head a few times is: When waking
a RT task is it better to:
1) run on current CPU if possible
2) run on CPU task previously ran on
I think #1 may result in lower latency. But, if the task has lots of
cache warmth the lower wakeup latency may be negated by running on a
'remote' cpu.
--
Mike
On Wed, Oct 10, 2007 at 09:22:48AM -0700, mike kravetz wrote:
> On Wed, Oct 10, 2007 at 10:49:35AM -0400, Gregory Haskins wrote:
> > diff --git a/kernel/sched.c b/kernel/sched.c
> > index 3e75c62..b7f7a96 100644
> > --- a/kernel/sched.c
> > +++ b/kernel/sched.c
> > @@ -1869,7 +1869,8 @@ out_activate:
> > * extra locking in this particular case, because
> > * we are on the current CPU.)
> > */
> > - if (TASK_PREEMPTS_CURR(p, this_rq))
> > + if (TASK_PREEMPTS_CURR(p, this_rq)
> > + && cpu_isset(this_cpu, p->cpus_allowed))
> > set_tsk_need_resched(this_rq->curr);
> > else
> > /*
>
> I wonder if it might better to explicitly take the rq lock and try to
> put the task on this_rq in this situation? Rather than waiting for
> schedule to pull it from a remote rq as part of balance_rt_tasks.
>
> A question that has passed through my head a few times is: When waking
> a RT task is it better to:
> 1) run on current CPU if possible
> 2) run on CPU task previously ran on
>
> I think #1 may result in lower latency. But, if the task has lots of
> cache warmth the lower wakeup latency may be negated by running on a
> 'remote' cpu.
Could we use task_hot() routine to find if the task is cache hot? If it
isn't, if possible, we could run on current CPU, else, if possible, on
the CPU it last ran on?
--
Regards,
Ankita Garg ([email protected])
Linux Technology Center
IBM India Systems & Technology Labs,
Bangalore, India