lkml.org 
[lkml]   [2016]   [Nov]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: task isolation discussion at Linux Plumbers
    Hi Paul,

    Just a couple of comments, but they be more suited to Andy.

    On Wed, Nov 09, 2016 at 09:38:08AM -0800, Paul E. McKenney wrote:
    > @@ -355,10 +373,33 @@ static bool rcu_dynticks_in_eqs_since(struct rcu_dynticks *rdtp, int snap)
    > static void rcu_dynticks_momentary_idle(void)
    > {
    > struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
    > - int special = atomic_add_return(2, &rdtp->dynticks);
    > + int special = atomic_add_return(2 * RCU_DYNTICK_CTRL_CTR,
    > + &rdtp->dynticks);
    >
    > /* It is illegal to call this from idle state. */
    > - WARN_ON_ONCE(!(special & 0x1));
    > + WARN_ON_ONCE(!(special & RCU_DYNTICK_CTRL_CTR));
    > +}
    > +
    > +/*
    > + * Set the special (bottom) bit of the specified CPU so that it
    > + * will take special action (such as flushing its TLB) on the
    > + * next exit from an extended quiescent state. Returns true if
    > + * the bit was successfully set, or false if the CPU was not in
    > + * an extended quiescent state.
    > + */

    Given that TLB maintenance on arm is handled in hardware (no need for IPI),
    I'd like to avoid this work if at all possible. However, without seeing the
    call site I can't tell if it's optional.

    > +bool rcu_eqs_special_set(int cpu)
    > +{
    > + int old;
    > + int new;
    > + struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
    > +
    > + do {
    > + old = atomic_read(&rdtp->dynticks);
    > + if (old & RCU_DYNTICK_CTRL_CTR)
    > + return false;
    > + new = old | RCU_DYNTICK_CTRL_MASK;
    > + } while (atomic_cmpxchg(&rdtp->dynticks, old, new) != old);
    > + return true;
    > }

    Can this be a cmpxchg_relaxed? What is it attempting to order?

    Will

    \
     
     \ /
      Last update: 2016-11-09 19:58    [W:2.874 / U:0.092 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site