Re: [RFC PATCH -rt 2/2] RCU priority boosting additions to rcutorture

[Paul E. McKenney]

On Thu, Feb 01, 2007 at 01:12:16PM +1100, Nigel Cunningham wrote:
> Hi Paul.
> 
> On Wed, 2007-01-31 at 17:26 -0800, Paul E. McKenney wrote:
> > This patch adds an optional preemption kernel thread to the rcutorture
> > tests.  This thread sets itself to a low RT priority and chews up CPU
> > in 10-second bursts, verifying that grace periods progress during this
> > 10-second interval.  Passes RCU torture testing on a 4-CPU (a pair of
> > 2-CPU dies) 64-bit Xeon system.
> 
> [...]
> 
> > Signed-off-by: Paul E. McKenney <[EMAIL PROTECTED]>
> > +static int rcu_torture_preempt(void *arg)
> > +{
> > +   int completedstart;
> > +   int err;
> > +   time_t gcstart;
> > +   struct sched_param sp;
> > +
> > +   sp.sched_priority = MAX_RT_PRIO - 1;
> > +   err = sched_setscheduler(current, SCHED_RR, &sp);
> > +   if (err != 0)
> > +           printk(KERN_ALERT "rcu_torture_preempt() priority err: %d\n",
> > +                  err);
> > +   current->flags |= PF_NOFREEZE;
> > +
> > +   do {
> > +           completedstart = rcu_torture_completed();
> > +           gcstart = xtime.tv_sec;
> > +           while ((xtime.tv_sec - gcstart < 10) &&
> > +                  (rcu_torture_completed() == completedstart))
> > +                   cond_resched();
> > +           if (rcu_torture_completed() == completedstart)
> > +                   rcu_torture_preempt_errors++;
> > +           schedule_timeout_interruptible(HZ);
> > +   } while (!kthread_should_stop());
> > +   return 0;
> > +}
> 
> Does it need to be NOFREEZE? I would think that it should be frozen
> during a suspend/hibernate.

Good to hear from you, Nigel!

Should indeed be OK to freeze during suspend/hibernate.  Will my
schedule_timeout_interruptible() be sufficient to allow the freeze
to happen, or do I need to add an explicit try_to_freeze()?

Ah, and I probably need to use the same trick that mtd_blktrans_thread()
does to avoid having all my sleeps killed of by an errant signal:

        spin_lock_irq(&current->sighand->siglock);
        sigfillset(&current->blocked);
        recalc_sigpending();
        spin_unlock_irq(&current->sighand->siglock);

Or is such paranoia unnecessary?

                                                        Thanx, Paul
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