If 'arat' is set in the cpuflags, we can avoid the checks for entering/exiting the tick broadcast code entirely. It would seem that this is a hot enough code path to make this worthwhile. I ran a few hackbench runs, and consistenly see reduced branches and cycles.
Signed-off-by: Jason Baron <[email protected]> --- drivers/idle/intel_idle.c | 29 ++++++++++++++++++++--------- 1 file changed, 20 insertions(+), 9 deletions(-) diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c index 4d140bb..61e965c 100644 --- a/drivers/idle/intel_idle.c +++ b/drivers/idle/intel_idle.c @@ -80,6 +80,8 @@ static unsigned int mwait_substates; #define LAPIC_TIMER_ALWAYS_RELIABLE 0xFFFFFFFF /* Reliable LAPIC Timer States, bit 1 for C1 etc. */ static unsigned int lapic_timer_reliable_states = (1 << 1); /* Default to only C1 */ +/* if arat is set no sense in checking on each c-state transition */ +static struct static_key lapic_timer_unreliable __read_mostly; struct idle_cpu { struct cpuidle_state *state_table; @@ -507,12 +509,10 @@ static int intel_idle(struct cpuidle_device *dev, { unsigned long ecx = 1; /* break on interrupt flag */ struct cpuidle_state *state = &drv->states[index]; - unsigned long eax = flg2MWAIT(state->flags); - unsigned int cstate; + unsigned long uninitialized_var(eax); + unsigned int uninitialized_var(cstate); int cpu = smp_processor_id(); - cstate = (((eax) >> MWAIT_SUBSTATE_SIZE) & MWAIT_CSTATE_MASK) + 1; - /* * leave_mm() to avoid costly and often unnecessary wakeups * for flushing the user TLB's associated with the active mm. @@ -520,13 +520,22 @@ static int intel_idle(struct cpuidle_device *dev, if (state->flags & CPUIDLE_FLAG_TLB_FLUSHED) leave_mm(cpu); - if (!(lapic_timer_reliable_states & (1 << (cstate)))) - clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &cpu); + if (static_key_false(&lapic_timer_unreliable)) { + eax = flg2MWAIT(state->flags); + cstate = (((eax) >> MWAIT_SUBSTATE_SIZE) & + MWAIT_CSTATE_MASK) + 1; + if (!(lapic_timer_reliable_states & (1 << (cstate)))) + clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, + &cpu); + } mwait_idle_with_hints(eax, ecx); - if (!(lapic_timer_reliable_states & (1 << (cstate)))) - clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &cpu); + if (static_key_false(&lapic_timer_unreliable)) { + if (!(lapic_timer_reliable_states & (1 << (cstate)))) + clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, + &cpu); + } return index; } @@ -702,8 +711,10 @@ static int __init intel_idle_probe(void) if (boot_cpu_has(X86_FEATURE_ARAT)) /* Always Reliable APIC Timer */ lapic_timer_reliable_states = LAPIC_TIMER_ALWAYS_RELIABLE; - else + else { + static_key_slow_inc(&lapic_timer_unreliable); on_each_cpu(__setup_broadcast_timer, (void *)true, 1); + } pr_debug(PREFIX "v" INTEL_IDLE_VERSION " model 0x%X\n", boot_cpu_data.x86_model); -- 1.8.2.rc2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
