From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Linux PM <linux-pm@vger.kernel.org>
Cc: Len Brown <len.brown@intel.com>,
LKML <linux-kernel@vger.kernel.org>,
Zhang Rui <rui.zhang@intel.com>,
"Rafael J. Wysocki" <rafael@kernel.org>,
Chen Yu <yu.c.chen@intel.com>
Subject: [PATCH 1/9] intel_idle: Simplify LAPIC timer reliability checks
Date: Thu, 13 Feb 2020 22:59:22 +0100 [thread overview]
Message-ID: <18406440.OXBZXsHz07@kreacher> (raw)
In-Reply-To: <2960689.qre192dJKD@kreacher>
From: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
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>
---
drivers/idle/intel_idle.c | 27 +++++++++++++--------------
1 file changed, 13 insertions(+), 14 deletions(-)
diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
index d55606608ac8..8d66efc53b89 100644
--- a/drivers/idle/intel_idle.c
+++ b/drivers/idle/intel_idle.c
@@ -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;
--
2.16.4
next prev parent reply other threads:[~2020-02-13 22:05 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-13 21:58 [PATCH 0/9] intel_idle: More assorted cleanups Rafael J. Wysocki
2020-02-13 21:59 ` Rafael J. Wysocki [this message]
2020-02-13 21:59 ` [PATCH 2/9] intel_idle: Clean up definitions of cpuidle callbacks Rafael J. Wysocki
2020-02-13 22:00 ` [PATCH 3/9] intel_idle: Relocate " Rafael J. Wysocki
2020-05-23 0:04 ` Qian Cai
2020-02-13 22:01 ` [PATCH 4/9] intel_idle: Add __initdata annotations to init time variables Rafael J. Wysocki
2020-02-13 22:01 ` [PATCH 5/9] intel_idle: Annotate init time data structures Rafael J. Wysocki
2020-02-13 22:02 ` [PATCH 6/9] intel_idle: Reorder declarations of static variables Rafael J. Wysocki
2020-02-13 22:03 ` [PATCH 7/9] intel_idle: Clean up kerneldoc comments of multiple functions Rafael J. Wysocki
2020-02-13 22:03 ` [PATCH 8/9] intel_idle: Define CPUIDLE_FLAG_TLB_FLUSHED as BIT(16) Rafael J. Wysocki
2020-02-13 22:04 ` [PATCH 9/9] intel_idle: Update copyright notice, known limitations and version Rafael J. Wysocki
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