From 74df0974b207189ac8335ae8113a8c1019a6ef5f Mon Sep 17 00:00:00 2001
From: ouyangxiangzhen <ouyangxiangzhen@xiaomi.com>
Date: Mon, 17 Jun 2024 18:31:06 +0800
Subject: [PATCH] arch/x86_64: Add ARCH_X86_64_IDLE_NOP and
 ARCH_X86_64_IDLE_MWAIT

Using the HLT instruction in VM usually traps into the Hypervisor and releases CPU control. This will result in real-time performance degradation. Using the NOP or MWAIT instruction for an IDLE loop can reduce energy consumption while not trapping into the Hypervisor.

Signed-off-by: ouyangxiangzhen <ouyangxiangzhen@xiaomi.com>
---
 arch/x86_64/src/common/Kconfig         | 32 ++++++++++++++++++++++++++
 arch/x86_64/src/intel64/intel64_idle.c | 20 +++++++++++++++-
 2 files changed, 51 insertions(+), 1 deletion(-)

diff --git a/arch/x86_64/src/common/Kconfig b/arch/x86_64/src/common/Kconfig
index a20a456a31..9effd0d296 100644
--- a/arch/x86_64/src/common/Kconfig
+++ b/arch/x86_64/src/common/Kconfig
@@ -35,6 +35,38 @@ config ARCH_X86_64_ACPI_BIOS
 
 endif # ARCH_X86_64_ACPI
 
+choice
+	prompt "x86_64 Idle Loop Options"
+	default ARCH_X86_64_IDLE_DEFAULT
+
+config ARCH_X86_64_IDLE_DEFAULT
+	bool "Idle Loop - HLT"
+	---help---
+		Use HLT instruction in IDLE loop.
+
+config ARCH_X86_64_IDLE_NOP
+	bool "Idle Loop - NOP"
+	---help---
+		Use NOP instruction in IDLE loop.
+		This can prevent VM exit in some virtualized environments,
+		thereby improving real-time performance.
+
+config ARCH_X86_64_IDLE_MWAIT
+	bool "Idle Loop - MWAIT"
+	---help---
+		Use MONITOR/MWAIT instruction in IDLE loop.
+
+endchoice # x86_64 Idle Loop Options
+
+config ARCH_X86_64_IDLE_MWAIT_ECX
+	hex "Idle MWAIT ECX value"
+	default 0x0
+	range 0x0 0xF
+	depends on ARCH_X86_64_IDLE_MWAIT
+	---help---
+		MWAIT ECX indicates the C-States
+		(0x0 for C1, 0x1 for C1E and so on).
+
 config ARCH_X86_64_HAVE_XSAVE
 	bool "XSAVE support"
 	default y
diff --git a/arch/x86_64/src/intel64/intel64_idle.c b/arch/x86_64/src/intel64/intel64_idle.c
index 2f56fdf1c0..53ed6db048 100644
--- a/arch/x86_64/src/intel64/intel64_idle.c
+++ b/arch/x86_64/src/intel64/intel64_idle.c
@@ -64,7 +64,25 @@ void up_idle(void)
    * "fake" timer interrupts. Hopefully, something will wake up.
    */
 
-  sched_process_timer();
+  nxsched_process_timer();
+#elif defined(CONFIG_ARCH_X86_64_IDLE_NOP)
+  asm volatile("nop");
+#elif defined(CONFIG_ARCH_X86_64_IDLE_MWAIT_ECX)
+  /* Dummy value to make MONITOR/MWAIT work */
+
+  int dummy;
+
+  /* MONITOR eax, ecx, edx */
+
+  asm volatile(".byte 0x0f, 0x01, 0xc8" ::
+                "a"(&dummy), "c"(0), "d"(0));
+
+  /* We enable sub C-state here and wait for interrupts */
+
+  /* MWAIT eax, ecx */
+
+  asm volatile(".byte 0x0f, 0x01, 0xc9" ::
+                "a"(0), "c"(CONFIG_ARCH_X86_64_IDLE_MWAIT_ECX));
 #else
   __asm__ volatile("hlt");
 #endif