lkml.org 
[lkml]   [2010]   [Jun]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH] rcutorture: add random preemption
    On Mon, Jun 21, 2010 at 06:50:11PM +0200, Peter Zijlstra wrote:
    > On Mon, 2010-06-21 at 09:43 -0700, Paul E. McKenney wrote:
    > > > +#ifdef CONFIG_PREEMPT
    > > > + if (!preempt_count() && !(rcu_random(rrsp) % (nrealreaders * 20000)))
    > > > + preempt_schedule();
    > > > +#endif
    > >
    > > This one scared me for a bit -- then I realized that preempt_schedule()
    > > won't actually schedule if preemption is in any way disabled. So the
    > > above really is OK, because Classic RCU and RCU-bh disable preemption.
    > >
    > > So, should we have a comment to this effect, or is my hypersensitivity to
    > > RCU semantics unique to me?
    >
    > Well it seems to do a !preempt_count() test too, so I wouldn't worry too
    > much about it, still using preempt_schedule() doesn't seem right, why
    > not use cond_resched()?

    My guess is that Lai wants to force a call to rcu_sched_qs() even if
    !need_resched(). One reason for doing this would be to put more stress
    on preemptible RCU's handling of context switches in RCU read-side
    critical sections.

    Another approach would be to have some high-priority threads that wake up
    periodically, as I plan to make rcutorture do for RCU priority boosting.
    Of course, this is not necessarily mutually exclusive with Lai's approach.

    Thanx, Paul


    \
     
     \ /
      Last update: 2010-06-21 19:07    [W:0.027 / U:30.660 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site