Date: Wed, 24 Jan 2007 12:37:57 +0800 From: David Xu <davidxu@freebsd.org> To: Jeff Roberson <jroberson@chesapeake.net> Cc: src-committers@freebsd.org, jhb@freebsd.org, cvs-src@freebsd.org, Jeff Roberson <jeff@freebsd.org>, cvs-all@freebsd.org, Julian Elischer <julian@freebsd.org> Subject: Re: cvs commit: src/sys/kern sched_ule.c Message-ID: <45B6E2A5.6080404@freebsd.org> In-Reply-To: <20070123200041.Y564@10.0.0.1> References: <200701230850.l0N8oZV2065483@repoman.freebsd.org> <200701241147.17846.davidxu@freebsd.org> <20070123200041.Y564@10.0.0.1>
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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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