On Fri, 6 Oct 2017 13:19:45 -0400 Jason Baron <[email protected]> wrote:
> If the 'arat' cpu flag is set, then the conditionals in intel_idle() > that guard calling tick_broadcast_enter()/exit() will never be true. > Use static_cpu_has(X86_FEATURE_ARAT) to create a fast path to replace > the conditional. > > Signed-off-by: Jason Baron <[email protected]> > Cc: Jacob Pan <[email protected]> > Cc: Len Brown <[email protected]> > Cc: Rafael J. Wysocki <[email protected]> > --- > drivers/idle/intel_idle.c | 16 +++++++++++----- > 1 file changed, 11 insertions(+), 5 deletions(-) > > diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c > index 5dc7ea4..5db5e31 100644 > --- a/drivers/idle/intel_idle.c > +++ b/drivers/idle/intel_idle.c > @@ -913,8 +913,7 @@ static __cpuidle int intel_idle(struct > cpuidle_device *dev, struct cpuidle_state *state = > &drv->states[index]; unsigned long eax = flg2MWAIT(state->flags); > unsigned int cstate; > - > - cstate = (((eax) >> MWAIT_SUBSTATE_SIZE) & > MWAIT_CSTATE_MASK) + 1; > + bool uninitialized_var(tick); > > /* > * NB: if CPUIDLE_FLAG_TLB_FLUSHED is set, this idle > transition @@ -923,12 +922,19 @@ static __cpuidle int > intel_idle(struct cpuidle_device *dev, > * useful with this knowledge. > */ > > - if (!(lapic_timer_reliable_states & (1 << (cstate)))) > - tick_broadcast_enter(); > + if (!static_cpu_has(X86_FEATURE_ARAT)) { > + cstate = (((eax) >> MWAIT_SUBSTATE_SIZE) & > + MWAIT_CSTATE_MASK) + 1; > + tick = false; > + if (!(lapic_timer_reliable_states & (1 << > (cstate)))) { > + tick = true; > + tick_broadcast_enter(); > + } > + } > > mwait_idle_with_hints(eax, ecx); > > - if (!(lapic_timer_reliable_states & (1 << (cstate)))) > + if (!static_cpu_has(X86_FEATURE_ARAT) && tick) > tick_broadcast_exit(); > > return index; Seems better to have a function pointer set up at init time to select whether we do tick_broadcast or not (two functions). There is no need to check CPU feature on every entry.
