Jeff Roberson wrote:
if idlethread is preempted, who will clear its idle bit in
idle_cpus_mask ?
idle_cpus_mask was broken before for all schedulers. This commit didn't
change that. ULE doesn't use idle_cpus_mask and it's idlethread doesn't
set or clear it. The idle thread for the other schedulers remains
unchanged.
I havn't read ULE code, but 4BSD has following code:
void
sched_idletd(void *dummy)
{
struct proc *p;
struct thread *td;
#ifdef SMP
cpumask_t mycpu;
#endif
td = curthread;
p = td->td_proc;
#ifdef SMP
mycpu = PCPU_GET(cpumask);
mtx_lock_spin(&sched_lock);
idle_cpus_mask |= mycpu;
mtx_unlock_spin(&sched_lock);
#endif
for (;;) {
mtx_assert(&Giant, MA_NOTOWNED);
how about if the idlethread is preempted here ? mycpu is not cleared.
while (sched_runnable() == 0)
cpu_idle();
mtx_lock_spin(&sched_lock);
#ifdef SMP
idle_cpus_mask &= ~mycpu;
#endif
mi_switch(SW_VOL, NULL);
#ifdef SMP
idle_cpus_mask |= mycpu;
#endif
mtx_unlock_spin(&sched_lock);
}
}
Julian wants to set idle_cpus_mask in sched_switch() which would make it
accurate no matter how idlethread switched out. that seems much more
reasonable to me.
I haven't seen sched_switch clears it, so at least, it should be fixed
for current 4BSD scheduler.
Cheers,
Jeff
Regards,
David Xu
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