On Mon, Nov 21, 2022 at 05:37:54PM -0800, Paul E. McKenney wrote:
> On Mon, Nov 21, 2022 at 11:51:40AM +0800, Zhouyi Zhou wrote:
> > @@ -358,7 +359,16 @@ torture_onoff(void *arg)
> > schedule_timeout_interruptible(HZ / 10);
> > continue;
> > }
> > +#ifdef CONFIG_NO_HZ_FULL
> > + /* do not offline tick do timer cpu */
> > + if (tick_nohz_full_running) {
> > + cpu = (torture_random(&rand) >> 4) % maxcpu;
> > + if (cpu >= tick_do_timer_cpu)
>
> Why is this ">=" instead of "=="?
>
> > + cpu = (cpu + 1) % (maxcpu + 1);
> > + } else
> > +#else
> > cpu = (torture_random(&rand) >> 4) % (maxcpu + 1);
> > +#endif
>
> What happens if the value of tick_do_timer_cpu changes between the time of
> the check above and the call to torture_offline() below? Alternatively,
> how is such a change in value prevented?
It can't, currently tick_do_timer_cpu is fixed when nohz_full is running.
It can however have special values at early boot such as TICK_DO_TIMER_NONE.
But if rcutorture is initialized after smp, it should be ok.
Thanks.
>
> Thanx, Paul
>
> > if (!torture_offline(cpu,
> > &n_offline_attempts, &n_offline_successes,
> > &sum_offline, &min_offline, &max_offline))
> > --
> > 2.34.1
> >
