linux-kernel - [PATCH v2] x86/acpi/cstate: Optimize ARB

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Message-ID: <1667792089-4904-1-git-send-email-TonyWWang-oc@zhaoxin.com>
Date:   Mon, 7 Nov 2022 11:34:49 +0800
From:   Tony W Wang-oc <TonyWWang-oc@...oxin.com>
To:     <rafael@...nel.org>, <len.brown@...el.com>, <pavel@....cz>,
        <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
        <dave.hansen@...ux.intel.com>, <x86@...nel.org>, <hpa@...or.com>,
        <linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     <linux-acpi@...r.kernel.org>, <CobeChen@...oxin.com>,
        <TimGuo@...oxin.com>, <LindaChai@...oxin.com>, <LeoLiu@...oxin.com>
Subject: [PATCH v2] x86/acpi/cstate: Optimize ARB_DISABLE on Centaur CPUs

On all recent Centaur platforms, ARB_DISABLE is handled by PMU
automatically while entering C3 type state. No need for OS to
issue the ARB_DISABLE, so set bm_control to zero to indicate that.

Signed-off-by: Tony W Wang-oc <TonyWWang-oc@...oxin.com>
---
Changes in V2:
 - fix typo in comments.
---
 arch/x86/kernel/acpi/cstate.c | 26 +++++++++++++++++---------
 1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/acpi/cstate.c b/arch/x86/kernel/acpi/cstate.c
index 7945eae..da71679 100644
--- a/arch/x86/kernel/acpi/cstate.c
+++ b/arch/x86/kernel/acpi/cstate.c
@@ -52,17 +52,25 @@ void acpi_processor_power_init_bm_check(struct acpi_processor_flags *flags,
 	if (c->x86_vendor == X86_VENDOR_INTEL &&
 	    (c->x86 > 0xf || (c->x86 == 6 && c->x86_model >= 0x0f)))
 			flags->bm_control = 0;
-	/*
-	 * For all recent Centaur CPUs, the ucode will make sure that each
-	 * core can keep cache coherence with each other while entering C3
-	 * type state. So, set bm_check to 1 to indicate that the kernel
-	 * doesn't need to execute a cache flush operation (WBINVD) when
-	 * entering C3 type state.
-	 */
+
 	if (c->x86_vendor == X86_VENDOR_CENTAUR) {
 		if (c->x86 > 6 || (c->x86 == 6 && c->x86_model == 0x0f &&
-		    c->x86_stepping >= 0x0e))
-			flags->bm_check = 1;
+		    c->x86_stepping >= 0x0e)) {
+			/*
+			 * For all recent Centaur CPUs, the ucode will make sure that each
+			 * core can keep cache coherence with each other while entering C3
+			 * type state. So, set bm_check to 1 to indicate that the kernel
+			 * doesn't need to execute a cache flush operation (WBINVD) when
+			 * entering C3 type state.
+			 */
+			flags->bm_check = 1;
+			/*
+			 * For all recent Centaur platforms, ARB_DISABLE is a nop.
+			 * Set bm_control to zero to indicate that ARB_DISABLE is
+			 * not required while entering C3 type state.
+			 */
+			flags->bm_control = 0;
+		}
 	}
 
 	if (c->x86_vendor == X86_VENDOR_ZHAOXIN) {
-- 
2.7.4