linux-kernel - [PATCH 1/3] x86/smp: Use static_call for arch_send_call_function_single

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Message-ID: <20251222201406.3725665-2-edumazet@google.com>
Date: Mon, 22 Dec 2025 20:14:04 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, Peter Zijlstra <peterz@...radead.org>, x86@...nel.org, 
	"H . Peter Anvin" <hpa@...or.com>
Cc: linux-kernel <linux-kernel@...r.kernel.org>, Eric Dumazet <eric.dumazet@...il.com>, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH 1/3] x86/smp: Use static_call for arch_send_call_function_single_ipi()

Use static_call to avoid an indirect call, especially expensive
with retpoline.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 arch/x86/include/asm/smp.h | 10 ++++++++--
 arch/x86/kernel/smp.c      | 10 ++++++++++
 arch/x86/xen/smp_hvm.c     |  1 +
 arch/x86/xen/smp_pv.c      |  1 +
 4 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
index 84951572ab8170578ca5c4a3437c66e9809f34c2..891a5d16bcd52d2da0b71d928d3728afe3d15ade 100644
--- a/arch/x86/include/asm/smp.h
+++ b/arch/x86/include/asm/smp.h
@@ -4,6 +4,7 @@
 #ifndef __ASSEMBLER__
 #include <linux/cpumask.h>
 #include <linux/thread_info.h>
+#include <linux/static_call_types.h>
 
 #include <asm/cpumask.h>
 
@@ -42,6 +43,12 @@ struct smp_ops {
 	void (*send_call_func_single_ipi)(int cpu);
 };
 
+void x86_smp_ops_static_call_update(void);
+
+void native_send_call_func_single_ipi(int cpu);
+DECLARE_STATIC_CALL(x86_send_call_func_single_ipi,
+		    native_send_call_func_single_ipi);
+
 /* Globals due to paravirt */
 extern void set_cpu_sibling_map(int cpu);
 
@@ -92,7 +99,7 @@ static inline void arch_smp_send_reschedule(int cpu)
 
 static inline void arch_send_call_function_single_ipi(int cpu)
 {
-	smp_ops.send_call_func_single_ipi(cpu);
+	static_call(x86_send_call_func_single_ipi)(cpu);
 }
 
 static inline void arch_send_call_function_ipi_mask(const struct cpumask *mask)
@@ -122,7 +129,6 @@ void __noreturn mwait_play_dead(unsigned int eax_hint);
 
 void native_smp_send_reschedule(int cpu);
 void native_send_call_func_ipi(const struct cpumask *mask);
-void native_send_call_func_single_ipi(int cpu);
 
 asmlinkage __visible void smp_reboot_interrupt(void);
 __visible void smp_reschedule_interrupt(struct pt_regs *regs);
diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index b014e6d229f9519add6f3fb315f1a2f375675a50..2c8fdf1f59d953e49a6beeba8f76f5fe62bd5db7 100644
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -300,6 +300,16 @@ struct smp_ops smp_ops = {
 };
 EXPORT_SYMBOL_GPL(smp_ops);
 
+DEFINE_STATIC_CALL(x86_send_call_func_single_ipi,
+		   native_send_call_func_single_ipi);
+
+void x86_smp_ops_static_call_update(void)
+{
+	static_call_update(x86_send_call_func_single_ipi,
+			   smp_ops.send_call_func_single_ipi);
+}
+EXPORT_SYMBOL_GPL(x86_smp_ops_static_call_update);
+
 int arch_cpu_rescan_dead_smt_siblings(void)
 {
 	enum cpuhp_smt_control old = cpu_smt_control;
diff --git a/arch/x86/xen/smp_hvm.c b/arch/x86/xen/smp_hvm.c
index 485c1d8804f739fbbb7980c98ed56eab59ad8b37..5ea0f53e4ea3f6cd4ad24fedbe2ef28d2dc444b9 100644
--- a/arch/x86/xen/smp_hvm.c
+++ b/arch/x86/xen/smp_hvm.c
@@ -85,4 +85,5 @@ void __init xen_hvm_smp_init(void)
 	smp_ops.smp_send_reschedule = xen_smp_send_reschedule;
 	smp_ops.send_call_func_ipi = xen_smp_send_call_function_ipi;
 	smp_ops.send_call_func_single_ipi = xen_smp_send_call_function_single_ipi;
+	x86_smp_ops_static_call_update();
 }
diff --git a/arch/x86/xen/smp_pv.c b/arch/x86/xen/smp_pv.c
index 9bb8ff8bff30a6d13a186609e40346203d4feb25..91f9d6854f7448bd1ffcb4e194615ce6336827bb 100644
--- a/arch/x86/xen/smp_pv.c
+++ b/arch/x86/xen/smp_pv.c
@@ -442,6 +442,7 @@ static const struct smp_ops xen_smp_ops __initconst = {
 void __init xen_smp_init(void)
 {
 	smp_ops = xen_smp_ops;
+	x86_smp_ops_static_call_update();
 
 	/* Avoid searching for BIOS MP tables */
 	x86_init.mpparse.find_mptable		= x86_init_noop;
-- 
2.52.0.351.gbe84eed79e-goog