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intel_idle: Simplify LAPIC timer reliability checks 

The lapic_timer_always_reliable variable really takes only two values
and some arithmetic in intel_idle() related to comparing it with the
target C-state's MWAIT hint value is unnecessary.

Simplify the code by replacing lapic_timer_always_reliable with
a bool variable lapic_timer_always_reliable and dropping the
LAPIC_TIMER_ALWAYS_RELIABLE symbol along with the excess
computations in intel_idle().

While at it, add a comment explaining the branch taken in intel_idle()
if the LAPIC timer is only reliable in C1 and modify the related debug
message in intel_idle_init() accordingly (the modification of this
message in the only expected functional impact of the change made
here).

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Rafael J. Wysocki 2020-02-06 18:40:54 +01:00
parent bb6d3fb354
commit 40ab82e08d
1 changed files with 13 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

27
drivers/idle/intel_idle.c
View File

@ -66,10 +66,7 @@ static int max_cstate = CPUIDLE_STATE_MAX - 1;
static unsigned int disabled_states_mask;
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 */
static bool lapic_timer_always_reliable;
struct idle_cpu {
struct cpuidle_state *state_table;
@ -908,7 +905,6 @@ static __cpuidle 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;
bool uninitialized_var(tick);
int cpu = smp_processor_id();
@ -919,13 +915,16 @@ static __cpuidle int intel_idle(struct cpuidle_device *dev,
if (state->flags & CPUIDLE_FLAG_TLB_FLUSHED)
leave_mm(cpu);
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)))) {
if (!static_cpu_has(X86_FEATURE_ARAT) && !lapic_timer_always_reliable) {
/*
* Switch over to one-shot tick broadcast if the target C-state
* is deeper than C1.
*/
if ((eax >> MWAIT_SUBSTATE_SIZE) & MWAIT_CSTATE_MASK) {
tick = true;
tick_broadcast_enter();
} else {
tick = false;
}
}
@ -1555,7 +1554,7 @@ static int intel_idle_cpu_online(unsigned int cpu)
{
struct cpuidle_device *dev;
if (lapic_timer_reliable_states != LAPIC_TIMER_ALWAYS_RELIABLE)
if (!lapic_timer_always_reliable)
tick_broadcast_enable();
/*
@ -1647,15 +1646,15 @@ static int __init intel_idle_init(void)
}
if (boot_cpu_has(X86_FEATURE_ARAT)) /* Always Reliable APIC Timer */
lapic_timer_reliable_states = LAPIC_TIMER_ALWAYS_RELIABLE;
lapic_timer_always_reliable = true;
retval = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "idle/intel:online",
intel_idle_cpu_online, NULL);
if (retval < 0)
goto hp_setup_fail;
pr_debug("lapic_timer_reliable_states 0x%x\n",
lapic_timer_reliable_states);
pr_debug("Local APIC timer is reliable in %s\n",
lapic_timer_always_reliable ? "all C-states" : "C1");
return 0;