linux-kernel - [PATCH 2/5] cpuidle: Introduce CPUIDLE_FLAG

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Message-ID: <20241206130408.18690-3-frederic@kernel.org>
Date: Fri,  6 Dec 2024 14:04:05 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Peter Zijlstra <peterz@...radead.org>,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	linux-pm@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Frederic Weisbecker <frederic@...nel.org>
Subject: [PATCH 2/5] cpuidle: Introduce CPUIDLE_FLAG_MWAIT

From: Peter Zijlstra <peterz@...radead.org>

Provide a way to tell the cpuidle core about states monitoring
TIF_NEED_RESCHED on the hardware level, monitor/mwait users being the
only examples in use.

This will allow cpuidle core to manage TIF_NR_POLLING on behalf of all
kinds of TIF_NEED_RESCHED watching states while keeping a necessary
distinction for the governors between software loops polling on
TIF_NEED_RESCHED and hardware monitored writes to thread flags.

[fweisbec: _ Initialize flag from acpi_processor_setup_cstates() instead
             of acpi_processor_setup_lpi_states(), as the latter seem to
             be about arm64...
           _ Rename CPUIDLE_FLAG_NO_IPI to CPUIDLE_FLAG_MWAIT]

Not-yet-signed-off-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
---
 drivers/acpi/processor_idle.c | 3 +++
 drivers/idle/intel_idle.c     | 5 ++++-
 include/linux/cpuidle.h       | 1 +
 3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index 698897b29de2..66cb5536d91e 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -806,6 +806,9 @@ static int acpi_processor_setup_cstates(struct acpi_processor *pr)
 		if (cx->type == ACPI_STATE_C1 || cx->type == ACPI_STATE_C2)
 			drv->safe_state_index = count;
 
+		if (cx->entry_method == ACPI_CSTATE_FFH)
+			state->flags |= CPUIDLE_FLAG_MWAIT;
+
 		/*
 		 * Halt-induced C1 is not good for ->enter_s2idle, because it
 		 * re-enables interrupts on exit.  Moreover, C1 is generally not
diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
index ac4d8faa3886..d52723fbeb04 100644
--- a/drivers/idle/intel_idle.c
+++ b/drivers/idle/intel_idle.c
@@ -1787,7 +1787,8 @@ static void __init intel_idle_init_cstates_acpi(struct cpuidle_driver *drv)
 		if (cx->type > ACPI_STATE_C1)
 			state->target_residency *= 3;
 
-		state->flags = MWAIT2flg(cx->address);
+		state->flags = MWAIT2flg(cx->address) | CPUIDLE_FLAG_MWAIT;
+
 		if (cx->type > ACPI_STATE_C2)
 			state->flags |= CPUIDLE_FLAG_TLB_FLUSHED;
 
@@ -2072,6 +2073,8 @@ static bool __init intel_idle_verify_cstate(unsigned int mwait_hint)
 
 static void state_update_enter_method(struct cpuidle_state *state, int cstate)
 {
+	state->flags |= CPUIDLE_FLAG_MWAIT;
+
 	if (state->flags & CPUIDLE_FLAG_INIT_XSTATE) {
 		/*
 		 * Combining with XSTATE with IBRS or IRQ_ENABLE flags
diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
index a9ee4fe55dcf..b8084617aa27 100644
--- a/include/linux/cpuidle.h
+++ b/include/linux/cpuidle.h
@@ -85,6 +85,7 @@ struct cpuidle_state {
 #define CPUIDLE_FLAG_OFF		BIT(4) /* disable this state by default */
 #define CPUIDLE_FLAG_TLB_FLUSHED	BIT(5) /* idle-state flushes TLBs */
 #define CPUIDLE_FLAG_RCU_IDLE		BIT(6) /* idle-state takes care of RCU */
+#define CPUIDLE_FLAG_MWAIT		BIT(7) /* hardware need_resched() monitoring */
 
 struct cpuidle_device_kobj;
 struct cpuidle_state_kobj;
-- 
2.46.0