linux-kernel - [PATCH v2] x86/apic: Inline __x2apic_send_IPI

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Message-ID: <20251223052026.4141498-1-edumazet@google.com>
Date: Tue, 23 Dec 2025 05:20:26 +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>, 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 v2] x86/apic: Inline __x2apic_send_IPI_dest()

Avoid one call/ret in networking RPS/RFS fast path, with no space cost.

scripts/bloat-o-meter -t vmlinux.before vmlinux.after
add/remove: 0/2 grow/shrink: 2/0 up/down: 96/-97 (-1)
Function                                     old     new   delta
x2apic_send_IPI                              146     198     +52
__x2apic_send_IPI_mask                       326     370     +44
__pfx___x2apic_send_IPI_dest                  16       -     -16
__x2apic_send_IPI_dest                        81       -     -81
Total: Before=20861234, After=20861233, chg -0.00%

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
v2: added CONFIG_X86_X2APIC dependency (kernel test robot), updated bloat-o-meter
v1: https://lore.kernel.org/lkml/CANn89iJ4r5hrqE=Lj16XVNFM7iZ+XB+JsXU8gE5ryeuG6kf1Sg@mail.gmail.com/T/#mc7288459ec504831a9888cb0e5c4dbdae253f263

 arch/x86/kernel/apic/local.h       | 10 +++++++++-
 arch/x86/kernel/apic/x2apic_phys.c |  6 ------
 2 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/apic/local.h b/arch/x86/kernel/apic/local.h
index bdcf609eb283..0e5dd6772d6a 100644
--- a/arch/x86/kernel/apic/local.h
+++ b/arch/x86/kernel/apic/local.h
@@ -14,7 +14,6 @@
 #include <asm/apic.h>
 
 /* X2APIC */
-void __x2apic_send_IPI_dest(unsigned int apicid, int vector, unsigned int dest);
 u32 x2apic_get_apic_id(u32 id);
 
 void x2apic_send_IPI_all(int vector);
@@ -42,6 +41,15 @@ static inline unsigned int __prepare_ICR(unsigned int shortcut, int vector,
 	return icr;
 }
 
+#ifdef CONFIG_X86_X2APIC
+static inline void __x2apic_send_IPI_dest(unsigned int apicid, int vector,
+					  unsigned int dest)
+{
+	unsigned long cfg = __prepare_ICR(0, vector, dest);
+	native_x2apic_icr_write(cfg, apicid);
+}
+#endif
+
 void default_init_apic_ldr(void);
 
 void apic_mem_wait_icr_idle(void);
diff --git a/arch/x86/kernel/apic/x2apic_phys.c b/arch/x86/kernel/apic/x2apic_phys.c
index 12d4c35547a6..10f79026e8e3 100644
--- a/arch/x86/kernel/apic/x2apic_phys.c
+++ b/arch/x86/kernel/apic/x2apic_phys.c
@@ -107,12 +107,6 @@ void x2apic_send_IPI_self(int vector)
 	apic_write(APIC_SELF_IPI, vector);
 }
 
-void __x2apic_send_IPI_dest(unsigned int apicid, int vector, unsigned int dest)
-{
-	unsigned long cfg = __prepare_ICR(0, vector, dest);
-	native_x2apic_icr_write(cfg, apicid);
-}
-
 static int x2apic_phys_probe(void)
 {
 	if (!x2apic_mode)
-- 
2.52.0.351.gbe84eed79e-goog