Re: [PATCH] SN2 user-MMIO CPU migration

Jack Steiner
2006-01-20T13:26:50Z

On Thu, Jan 19, 2006 at 06:18:43PM -0800, Jesse Barnes wrote:
> On Thursday, January 19, 2006 4:06 pm, Brent Casavant wrote:
> > #ifndef __ARCH_WANT_UNLOCKED_CTXSW
> > static inline int task_running(runqueue_t *rq, task_t *p)
> > @@ -936,6 +939,7 @@ static int migrate_task(task_t *p, int d
> > * it is sufficient to simply update the task's cpu field.
> > */
> > if (!p->array && !task_running(rq, p)) {
> > + arch_task_migrate(p);
> > set_task_cpu(p, dest_cpu);
> > return 0;
> > }
> > @@ -1353,6 +1357,7 @@ static int try_to_wake_up(task_t *p, uns
> > out_set_cpu:
> > new_cpu = wake_idle(new_cpu, p);
> > if (new_cpu != cpu) {
> > + arch_task_migrate(p);
> > set_task_cpu(p, new_cpu);
> > task_rq_unlock(rq, &flags);
> > /* might preempt at this point */
> > @@ -1876,6 +1881,7 @@ void pull_task(runqueue_t *src_rq, prio_
> > {
> > dequeue_task(p, src_array);
> > dec_nr_running(p, src_rq);
> > + arch_task_migrate(p);
> > set_task_cpu(p, this_cpu);
> > inc_nr_running(p, this_rq);
> > enqueue_task(p, this_array);
> > @@ -4547,6 +4553,7 @@ static void __migrate_task(struct task_s
> > if (!cpu_isset(dest_cpu, p->cpus_allowed))
> > goto out;
> >
> > + arch_task_migrate(p);
> > set_task_cpu(p, dest_cpu);
> > if (p->array) {
> > /*
>
> Maybe you could just turn the above into mmiowb() calls instead? That
> would cover altix, origin, and ppc as well I think. On other platforms
> it would be a complete no-op.
>
> Jesse

I don't think calling mmiob() directly would work. In order to make
CONFIG_IA64_GENERIC work, the call to mmiob() needs to be underneath a
platform vector. Using ia64_platform_is() would also work but I think
a platform vector is cleaner.

A second reason for an arch_task_migrate() instead of a specific mmiob() is
to provide a hook for a future platform that require additional work
to be done when a task migrates.

--
Thanks

Jack Steiner (steiner@sgi.com) 651-683-5302