Messages in this thread | | | Subject | Re: [PATCH 09/32] nohz/cpuset: Restart tick when nohz flag is cleared on cpuset | From | Steven Rostedt <> | Date | Tue, 30 Oct 2012 14:55:00 -0400 |
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On Mon, 2012-10-29 at 16:27 -0400, Steven Rostedt wrote: > plain text document attachment > (0009-nohz-cpuset-Restart-tick-when-nohz-flag-is-cleared-o.patch) > From: Frederic Weisbecker <fweisbec@gmail.com> > > Issue an IPI to restart the tick on a CPU that belongs > to a cpuset when its nohz flag gets cleared. > > Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> > Cc: Alessio Igor Bogani <abogani@kernel.org> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Avi Kivity <avi@redhat.com> > Cc: Chris Metcalf <cmetcalf@tilera.com> > Cc: Christoph Lameter <cl@linux.com> > Cc: Daniel Lezcano <daniel.lezcano@linaro.org> > Cc: Geoff Levand <geoff@infradead.org> > Cc: Gilad Ben Yossef <gilad@benyossef.com> > Cc: Hakan Akkan <hakanakkan@gmail.com> > Cc: Ingo Molnar <mingo@kernel.org> > Cc: Kevin Hilman <khilman@ti.com> > Cc: Max Krasnyansky <maxk@qualcomm.com> > Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Stephen Hemminger <shemminger@vyatta.com> > Cc: Steven Rostedt <rostedt@goodmis.org> > Cc: Sven-Thorsten Dietrich <thebigcorporation@gmail.com> > Cc: Thomas Gleixner <tglx@linutronix.de> > --- > include/linux/cpuset.h | 2 ++ > kernel/cpuset.c | 25 +++++++++++++++++++++++-- > kernel/time/tick-sched.c | 8 ++++++++ > 3 files changed, 33 insertions(+), 2 deletions(-) > > diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h > index 7e7eb41..631968b 100644 > --- a/include/linux/cpuset.h > +++ b/include/linux/cpuset.h > @@ -260,6 +260,8 @@ static inline bool cpuset_adaptive_nohz(void) > */ > return cpuset_cpu_adaptive_nohz(smp_processor_id()); > } > + > +extern void cpuset_exit_nohz_interrupt(void *unused); > #else > static inline bool cpuset_cpu_adaptive_nohz(int cpu) { return false; } > static inline bool cpuset_adaptive_nohz(void) { return false; } > diff --git a/kernel/cpuset.c b/kernel/cpuset.c > index 6319d8e..1b67e5b 100644 > --- a/kernel/cpuset.c > +++ b/kernel/cpuset.c > @@ -1200,6 +1200,14 @@ static void cpuset_change_flag(struct task_struct *tsk, > > DEFINE_PER_CPU(atomic_t, cpu_adaptive_nohz_ref); > > +static void cpu_exit_nohz(int cpu) > +{ > + preempt_disable(); > + smp_call_function_single(cpu, cpuset_exit_nohz_interrupt, > + NULL, true); > + preempt_enable(); > +} > + > static void update_nohz_cpus(struct cpuset *old_cs, struct cpuset *cs) > { > int cpu; > @@ -1211,9 +1219,22 @@ static void update_nohz_cpus(struct cpuset *old_cs, struct cpuset *cs) > for_each_cpu(cpu, cs->cpus_allowed) { > atomic_t *ref = &per_cpu(cpu_adaptive_nohz_ref, cpu); > if (is_adaptive_nohz(cs)) > - atomic_inc(ref); > + val = atomic_inc_return(ref); > else > - atomic_dec(ref); > + val = atomic_dec_return(ref); > + > + if (!val) { > + /* > + * The update to cpu_adaptive_nohz_ref must be > + * visible right away. So that once we restart the tick > + * from the IPI, it won't be stopped again due to cache > + * update lag. > + * FIXME: We probably need more to ensure this value is really > + * visible right away.
What more do you want? stomp_machine()??
> + */ > + smp_mb();
The atomic_inc_return() and atomic_dec_return() already imply a smp_mb().
Later patches change this code, so I wont dwell on this patch too much.
> + cpu_exit_nohz(cpu); > + } > } > } > #else > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > index 0a5e650..de7de68 100644 > --- a/kernel/time/tick-sched.c > +++ b/kernel/time/tick-sched.c > @@ -884,6 +884,14 @@ void tick_nohz_check_adaptive(void) > } > } > > +void cpuset_exit_nohz_interrupt(void *unused) > +{ > + struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); > + > + if (ts->tick_stopped && !is_idle_task(current)) > + tick_nohz_restart_adaptive();
BTW, what a confusing name. "restart_adaptive()"? It sounds like we are going to restart the adaptive code, like restarting NOHZ.
-- Steve
> +} > + > void tick_nohz_post_schedule(void) > { > struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
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