Re: kern/40419 (processor sets broken on 5.99.6)

[Mindaugas Rasiukevicius <rmind%netbsd.org@localhost>]

Andrew Doran <ad%netbsd.org@localhost> wrote:
> > > I was thinking of a function that scans all threads, with cpu_lock
> > > held, and checks to see if their l_cpu is allowed by their affinity
> > > mask, processor set or LP_BOUND flag. If not, change l_cpu (or migrate
> > > if online), then do a broadcast xcall to nullop() if there have been
> > > migrations.
> > 
> > After some thinking, I do not think it is worth. Theoretically,
> > xc_broadcast might still not ensure that all LWPs have migrated, eg. in a
> > case when there are many migrating LWPs in the same run-queue.
> 
> Hmm. I can't look at the code right now. If we can have LWPs in the wrong
> runqueue after a pset/affinity change, we should move them to prevent them
> running on that CPU after there is a context switch. Maybe it would be
> useful to add a syncobj_t::sobj_changecpu()?

It would not migrate immediately only if LWP is in LSRUN (and if it's in the
runqueue) or LSONPROC state. For both cases LWP would migrate just after the
context-switch via idle loop (l_target_cpu != NULL).

If we really want to be synchronous about this, then a simple cv_wait() in
lwp_migrate() and cv_broadcast() in sched_idle() would work. Do you see some
good reason to do this?

-- 
Best regards,
Mindaugas