On Friday, May 11, 2012, Colin Cross wrote:
> On Wed, May 9, 2012 at 2:31 PM, Rafael J. Wysocki <rjw@xxxxxxx> wrote:
> > On Tuesday, May 08, 2012, Colin Cross wrote:
> >> Adds cpuidle_coupled_parallel_barrier, which can be used by coupled
> >> cpuidle state enter functions to handle resynchronization after
> >> determining if any cpu needs to abort. The normal use case will
> >> be:
> >>
> >> static bool abort_flag;
> >> static atomic_t abort_barrier;
> >>
> >> int arch_cpuidle_enter(struct cpuidle_device *dev, ...)
> >> {
> >> if (arch_turn_off_irq_controller()) {
> >> /* returns an error if an irq is pending and would be lost
> >> if idle continued and turned off power */
> >> abort_flag = true;
> >> }
> >>
> >> cpuidle_coupled_parallel_barrier(dev, &abort_barrier);
> >>
> >> if (abort_flag) {
> >> /* One of the cpus didn't turn off it's irq controller */
> >> arch_turn_on_irq_controller();
> >> return -EINTR;
> >> }
> >>
> >> /* continue with idle */
> >> ...
> >> }
> >>
> >> This will cause all cpus to abort idle together if one of them needs
> >> to abort.
> >>
> >> Reviewed-by: Santosh Shilimkar <santosh.shilimkar@xxxxxx>
> >> Tested-by: Santosh Shilimkar <santosh.shilimkar@xxxxxx>
> >> Reviewed-by: Kevin Hilman <khilman@xxxxxx>
> >> Tested-by: Kevin Hilman <khilman@xxxxxx>
> >> Signed-off-by: Colin Cross <ccross@xxxxxxxxxxx>
> >> ---
> >> drivers/cpuidle/coupled.c | 37 +++++++++++++++++++++++++++++++++++++
> >> include/linux/cpuidle.h | 4 ++++
> >> 2 files changed, 41 insertions(+), 0 deletions(-)
> >>
> >> diff --git a/drivers/cpuidle/coupled.c b/drivers/cpuidle/coupled.c
> >> index 93101fb..3e65de1 100644
> >> --- a/drivers/cpuidle/coupled.c
> >> +++ b/drivers/cpuidle/coupled.c
> >> @@ -130,6 +130,43 @@ struct cpuidle_coupled {
> >> static cpumask_t cpuidle_coupled_poked_mask;
> >>
> >> /**
> >> + * cpuidle_coupled_parallel_barrier - synchronize all online coupled cpus
> >> + * @dev: cpuidle_device of the calling cpu
> >> + * @a: atomic variable to hold the barrier
> >> + *
> >> + * No caller to this function will return from this function until all online
> >> + * cpus in the same coupled group have called this function. Once any caller
> >> + * has returned from this function, the barrier is immediately available for
> >> + * reuse.
> >> + *
> >> + * The atomic variable a must be initialized to 0 before any cpu calls
> >> + * this function, will be reset to 0 before any cpu returns from this function.
> >> + *
> >> + * Must only be called from within a coupled idle state handler
> >> + * (state.enter when state.flags has CPUIDLE_FLAG_COUPLED set).
> >> + *
> >> + * Provides full smp barrier semantics before and after calling.
> >> + */
> >> +void cpuidle_coupled_parallel_barrier(struct cpuidle_device *dev, atomic_t *a)
> >> +{
> >> + int n = dev->coupled->online_count;
> >> +
> >> + smp_mb__before_atomic_inc();
> >> + atomic_inc(a);
> >> +
> >> + while (atomic_read(a) < n)
> >> + cpu_relax();
> >> +
> >> + if (atomic_inc_return(a) == n * 2) {
> >> + atomic_set(a, 0);
> >> + return;
> >> + }
> >> +
> >> + while (atomic_read(a) > n)
> >> + cpu_relax();
> >> +}
> >
> > Well, this looks like "wait until all CPUs execute this code". Don't we have
> > anything like this already somewhere?
> >
> >> +
> >> +/**
> >> * cpuidle_state_is_coupled - check if a state is part of a coupled set
> >> * @dev: struct cpuidle_device for the current cpu
> >> * @drv: struct cpuidle_driver for the platform
> >> diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
> >> index 6038448..5ab7183 100644
> >> --- a/include/linux/cpuidle.h
> >> +++ b/include/linux/cpuidle.h
> >> @@ -183,6 +183,10 @@ static inline int cpuidle_wrap_enter(struct cpuidle_device *dev,
> >>
> >> #endif
> >>
> >> +#ifdef CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED
> >> +void cpuidle_coupled_parallel_barrier(struct cpuidle_device *dev, atomic_t *a);
> >> +#endif
> >
> > Why exactly is the extra Kconfig option necessary?
>
> It prevents compiling in coupled.o (2k text section) on the majority
> of kernels that will never use it.
OK, sorry, for some unknown reason it seemed to me that the option was added by
this patch.
Thanks,
Rafael
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