| Message ID | 1346360743-3628-3-git-send-email-paulmck@linux.vnet.ibm.com |
|---|---|
| State | Accepted |
| Commit | 9a0c6fef423528ba5b62aa31b29aabf689eb8f70 |
| Headers | show |
On Thu, Aug 30, 2012 at 02:05:20PM -0700, Paul E. McKenney wrote: > From: "Paul E. McKenney" <paul.mckenney@linaro.org> > > The current implementation of RCU_FAST_NO_HZ tries reasonably hard to rid > the current CPU of RCU callbacks. This is appropriate when the CPU is > entering idle, where it doesn't have much useful to do anyway, but is most > definitely not what you want when transitioning to user-mode execution. > This commit therefore detects the adaptive-tick case, and refrains from > burning CPU time getting rid of RCU callbacks in that case. With the OOM handler from your other patch series, I don't know that it makes as much sense in the idle case, either; perhaps it would make more sense to wait and batch up more callbacks as long as you have memory, and then run them in one big burst. > Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org> > kernel/rcutree_plugin.h | 20 ++++++++++++++++++++ > 1 files changed, 20 insertions(+), 0 deletions(-) > > diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h > index 7f3244c..b0f09d6 100644 > --- a/kernel/rcutree_plugin.h > +++ b/kernel/rcutree_plugin.h > @@ -1997,6 +1997,26 @@ static void rcu_prepare_for_idle(int cpu) > if (!tne) > return; > > + /* Adaptive-tick mode, where usermode execution is idle to RCU. */ > + if (!is_idle_task(current)) { > + rdtp->dyntick_holdoff = jiffies - 1; > + if (rcu_cpu_has_nonlazy_callbacks(cpu)) { > + trace_rcu_prep_idle("User dyntick with callbacks"); > + rdtp->idle_gp_timer_expires = > + round_up(jiffies + RCU_IDLE_GP_DELAY, > + RCU_IDLE_GP_DELAY); > + } else if (rcu_cpu_has_callbacks(cpu)) { > + rdtp->idle_gp_timer_expires = > + round_jiffies(jiffies + RCU_IDLE_LAZY_GP_DELAY); > + trace_rcu_prep_idle("User dyntick with lazy callbacks"); > + } else { > + return; > + } > + tp = &rdtp->idle_gp_timer; > + mod_timer_pinned(tp, rdtp->idle_gp_timer_expires); > + return; > + } > + > /* > * If this is an idle re-entry, for example, due to use of > * RCU_NONIDLE() or the new idle-loop tracing API within the idle > -- > 1.7.8 >
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 7f3244c..b0f09d6 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -1997,6 +1997,26 @@ static void rcu_prepare_for_idle(int cpu) if (!tne) return; + /* Adaptive-tick mode, where usermode execution is idle to RCU. */ + if (!is_idle_task(current)) { + rdtp->dyntick_holdoff = jiffies - 1; + if (rcu_cpu_has_nonlazy_callbacks(cpu)) { + trace_rcu_prep_idle("User dyntick with callbacks"); + rdtp->idle_gp_timer_expires = + round_up(jiffies + RCU_IDLE_GP_DELAY, + RCU_IDLE_GP_DELAY); + } else if (rcu_cpu_has_callbacks(cpu)) { + rdtp->idle_gp_timer_expires = + round_jiffies(jiffies + RCU_IDLE_LAZY_GP_DELAY); + trace_rcu_prep_idle("User dyntick with lazy callbacks"); + } else { + return; + } + tp = &rdtp->idle_gp_timer; + mod_timer_pinned(tp, rdtp->idle_gp_timer_expires); + return; + } + /* * If this is an idle re-entry, for example, due to use of * RCU_NONIDLE() or the new idle-loop tracing API within the idle