linux-kernel - [patch 16/18] x86/apic: Convert 32bit to IPI shorthand static key

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Date:   Wed, 03 Jul 2019 12:54:47 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Nadav Amit <namit@...are.com>,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Stephane Eranian <eranian@...gle.com>,
        Feng Tang <feng.tang@...el.com>
Subject: [patch 16/18] x86/apic: Convert 32bit to IPI shorthand static key

Broadcast now depends on the fact that all present CPUs have been booted
once so handling broadcast IPIs is not doing any harm. In case that a CPU
is offline, it does not react to regular IPIs and the NMI handler returns
early.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 arch/x86/kernel/apic/ipi.c |   12 +++---------
 1 file changed, 3 insertions(+), 9 deletions(-)

--- a/arch/x86/kernel/apic/ipi.c
+++ b/arch/x86/kernel/apic/ipi.c
@@ -8,13 +8,7 @@
 DEFINE_STATIC_KEY_FALSE(apic_use_ipi_shorthand);
 
 #ifdef CONFIG_SMP
-#ifdef CONFIG_HOTPLUG_CPU
-#define DEFAULT_SEND_IPI	(1)
-#else
-#define DEFAULT_SEND_IPI	(0)
-#endif
-
-static int apic_ipi_shorthand_off __ro_after_init = DEFAULT_SEND_IPI;
+static int apic_ipi_shorthand_off __ro_after_init;
 
 static __init int apic_ipi_shorthand(char *str)
 {
@@ -250,7 +244,7 @@ void default_send_IPI_allbutself(int vec
 	if (num_online_cpus() < 2)
 		return;
 
-	if (apic_ipi_shorthand_off || vector == NMI_VECTOR) {
+	if (static_branch_likely(&apic_use_ipi_shorthand)) {
 		apic->send_IPI_mask_allbutself(cpu_online_mask, vector);
 	} else {
 		__default_send_IPI_shortcut(APIC_DEST_ALLBUT, vector);
@@ -259,7 +253,7 @@ void default_send_IPI_allbutself(int vec
 
 void default_send_IPI_all(int vector)
 {
-	if (apic_ipi_shorthand_off || vector == NMI_VECTOR) {
+	if (static_branch_likely(&apic_use_ipi_shorthand)) {
 		apic->send_IPI_mask(cpu_online_mask, vector);
 	} else {
 		__default_send_IPI_shortcut(APIC_DEST_ALLINC, vector);