linux-kernel - [PATCH v2 2/2] intel_idle: Add a new flag to initialize the AMX state

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Date:   Wed,  9 Mar 2022 14:34:31 -0800
From:   "Chang S. Bae" <chang.seok.bae@...el.com>
To:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-pm@...r.kernel.org
Cc:     tglx@...utronix.de, dave.hansen@...ux.intel.com,
        peterz@...radead.org, bp@...en8.de, rafael@...nel.org,
        ravi.v.shankar@...el.com, chang.seok.bae@...el.com,
        Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>
Subject: [PATCH v2 2/2] intel_idle: Add a new flag to initialize the AMX state

The non-initialized AMX state can be the cause of C-state demotion from C6
to C1E. This low-power idle state may improve power savings and thus result
in a higher available turbo frequency budget.

This behavior is implementation-specific. Initialize the state for the C6
entrance of Sapphire Rapids as needed.

Suggested-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Chang S. Bae <chang.seok.bae@...el.com>
Tested-by : Zhang Rui <rui.zhang@...el.com>
Cc: Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>
Cc: linux-pm@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
---
Changes from v1:
* Simplify the code with a new flag (Rui).
* Rebase on Artem's patches for SPR intel_idle.
* Massage the changelog.

Dependency on the new C-state table for SPR:
https://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git/commit/?h=linux-next&id=9edf3c0ffef0ec1bed8300315852b5c6a0997130
---
 drivers/idle/intel_idle.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
index 1c7c25909e54..6ecbeffdf785 100644
--- a/drivers/idle/intel_idle.c
+++ b/drivers/idle/intel_idle.c
@@ -54,6 +54,7 @@
 #include <asm/intel-family.h>
 #include <asm/mwait.h>
 #include <asm/msr.h>
+#include <asm/fpu/api.h>
 
 #define INTEL_IDLE_VERSION "0.5.1"
 
@@ -99,6 +100,11 @@ static unsigned int mwait_substates __initdata;
  */
 #define CPUIDLE_FLAG_ALWAYS_ENABLE	BIT(15)
 
+/*
+ * Initialize large xstate for the C6-state entrance.
+ */
+#define CPUIDLE_FLAG_INIT_XSTATE	BIT(16)
+
 /*
  * MWAIT takes an 8-bit "hint" in EAX "suggesting"
  * the C-state (top nibble) and sub-state (bottom nibble)
@@ -136,6 +142,9 @@ static __cpuidle int intel_idle(struct cpuidle_device *dev,
 	if (state->flags & CPUIDLE_FLAG_IRQ_ENABLE)
 		local_irq_enable();
 
+	if (state->flags & CPUIDLE_FLAG_INIT_XSTATE)
+		fpu_idle_fpregs();
+
 	mwait_idle_with_hints(eax, ecx);
 
 	return index;
@@ -156,8 +165,12 @@ static __cpuidle int intel_idle(struct cpuidle_device *dev,
 static __cpuidle int intel_idle_s2idle(struct cpuidle_device *dev,
 				       struct cpuidle_driver *drv, int index)
 {
-	unsigned long eax = flg2MWAIT(drv->states[index].flags);
 	unsigned long ecx = 1; /* break on interrupt flag */
+	struct cpuidle_state *state = &drv->states[index];
+	unsigned long eax = flg2MWAIT(state->flags);
+
+	if (state->flags & CPUIDLE_FLAG_INIT_XSTATE)
+		fpu_idle_fpregs();
 
 	mwait_idle_with_hints(eax, ecx);
 
@@ -792,7 +805,8 @@ static struct cpuidle_state spr_cstates[] __initdata = {
 	{
 		.name = "C6",
 		.desc = "MWAIT 0x20",
-		.flags = MWAIT2flg(0x20) | CPUIDLE_FLAG_TLB_FLUSHED,
+		.flags = MWAIT2flg(0x20) | CPUIDLE_FLAG_TLB_FLUSHED | \
+					   CPUIDLE_FLAG_INIT_XSTATE,
 		.exit_latency = 290,
 		.target_residency = 800,
 		.enter = &intel_idle,
-- 
2.17.1