[9fans] run queues

[Philippe Anel <xigh@bouyapop.org>]

Hi 9fans,

While reading src/9/port/proc.c:^runproc, I realized that the
following code is called without any lock. I would expect one in order
to walk through the each rq lists, as it is called with interrupt
enabled.

I think this would not crash the system because procs are not
dynamically allocated or freed.

I also know that locking can be a problem regarding performance.

        for(rq = &runq[Nrq-1]; rq >= runq; rq--){
            for(p = rq->head; p; p = p->rnext){
                if(p->mp == nil || p->mp == MACHP(m->machno)
                || (!p->wired && i > 0))
                    goto found;
            }
        }

What do you think ?

Phil;

Ps: It seems runqs were designed to be individually locked. Is there
any info about the reason why all the runq are locked at once using :

    lock(runq);
    // ...
    unlock(runq);

where we could expect (with some other changes of course) :

    lock(rq);
    // ...
    unlock(rq);

?