linux-kernel - [tip: x86/fpu] intel_idle: Add a new flag to initialize the AMX state

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Date:   Wed, 08 Jun 2022 19:32:37 -0000
From:   "tip-bot2 for Chang S. Bae" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Zhang Rui <rui.zhang@...el.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        "Chang S. Bae" <chang.seok.bae@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/fpu] intel_idle: Add a new flag to initialize the AMX state

The following commit has been merged into the x86/fpu branch of tip:

Commit-ID:     43843d58393026fef4a43d192b641a4fabdc42bf
Gitweb:        https://git.kernel.org/tip/43843d58393026fef4a43d192b641a4fabdc42bf
Author:        Chang S. Bae <chang.seok.bae@...el.com>
AuthorDate:    Wed, 08 Jun 2022 09:47:48 -07:00
Committer:     Dave Hansen <dave.hansen@...ux.intel.com>
CommitterDate: Wed, 08 Jun 2022 12:04:11 -07:00

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.

Tested-by : Zhang Rui <rui.zhang@...el.com>
Suggested-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Chang S. Bae <chang.seok.bae@...el.com>
Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Link: https://lkml.kernel.org/r/20220608164748.11864-3-chang.seok.bae@intel.com
---
 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 b7640cf..d357908 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"
 
@@ -101,6 +102,11 @@ 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)
  * 0x00 means "MWAIT(C1)", 0x10 means "MWAIT(C2)" etc.
@@ -134,6 +140,9 @@ 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;
@@ -154,8 +163,12 @@ 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);
 
@@ -790,7 +803,8 @@ 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,