linux-kernel - [PATCH v3] Optimize C3 entry on Centaur CPUs

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Date:   Tue, 29 May 2018 18:12:37 +0800
From:   David Wang <davidwang@...oxin.com>
To:     <rjw@...ysocki.net>, <mingo@...hat.com>, <len.brown@...el.com>,
        <pavel@....cz>, <tglx@...utronix.de>, <hpa@...or.com>,
        <x86@...nel.org>, <linux-pm@...nel.org>,
        <linux-kernel@...r.kernel.org>
CC:     <brucechang@...-alliance.com>, <cooperyan@...oxin.com>,
        <qiyuanwang@...oxin.com>, <benjaminpan@...tech.com>,
        <lukelin@...cpu.com>, <timguo@...oxin.com>,
        David Wang <davidwang@...oxin.com>
Subject: [PATCH v3] Optimize C3 entry on Centaur CPUs

For new Centaur CPUs the ucode will take care of the preservation of cache coherence
between CPU cores in C-states regardless of how deep the C-states are. So, it is not
necessary to flush the caches in software befor entering C3.

Signed-off-by: David Wang <davidwang@...oxin.com>

Changes from v2 to v3:
*1, Replace "c->x86_mask" with "c->x86_stepping".

Changes from v1 to v2:
* 1, Add some Family/Model/Stepping contrains to let this patch only apply
* to new centaur CPUs.
* 2, The arbiter disable/enable operations maybe needed for old VIA/Centaur
* platform. So, delete "flags->bm_control=0" in patch v1.

---
 arch/x86/kernel/acpi/cstate.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/x86/kernel/acpi/cstate.c b/arch/x86/kernel/acpi/cstate.c
index dde437f..a82fed6 100644
--- a/arch/x86/kernel/acpi/cstate.c
+++ b/arch/x86/kernel/acpi/cstate.c
@@ -51,6 +51,19 @@ 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
+	 * need not 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;
+	}
 }
 EXPORT_SYMBOL(acpi_processor_power_init_bm_check);
 
-- 
1.9.1