linux-kernel - [PATCH v2 3/5] x86/percpu, x86/irq: Relax {set,get}_irq

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Date:   Thu, 13 Jun 2019 15:54:48 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     torvalds@...ux-foundation.org, mingo@...nel.org, bp@...en8.de,
        tglx@...utronix.de, luto@...nel.org, namit@...are.com,
        peterz@...radead.org
Cc:     linux-kernel@...r.kernel.org, Nadav Amit <nadav.amit@...il.com>
Subject: [PATCH v2 3/5] x86/percpu, x86/irq: Relax {set,get}_irq_regs()

Nadav reported that since the this_cpu_*() ops got asm-volatile
constraints on, code generation suffered for do_IRQ(), but since this
is all with IRQs disabled we can use __this_cpu_*().

smp_x86_platform_ipi                                      234        222   -12,+0
smp_kvm_posted_intr_ipi                                    74         66   -8,+0
smp_kvm_posted_intr_wakeup_ipi                             86         78   -8,+0
smp_apic_timer_interrupt                                  292        284   -8,+0
smp_kvm_posted_intr_nested_ipi                             74         66   -8,+0
do_IRQ                                                    195        187   -8,+0

Reported-by: Nadav Amit <nadav.amit@...il.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/include/asm/irq_regs.h |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/arch/x86/include/asm/irq_regs.h
+++ b/arch/x86/include/asm/irq_regs.h
@@ -16,7 +16,7 @@ DECLARE_PER_CPU(struct pt_regs *, irq_re
 
 static inline struct pt_regs *get_irq_regs(void)
 {
-	return this_cpu_read(irq_regs);
+	return __this_cpu_read(irq_regs);
 }
 
 static inline struct pt_regs *set_irq_regs(struct pt_regs *new_regs)
@@ -24,7 +24,7 @@ static inline struct pt_regs *set_irq_re
 	struct pt_regs *old_regs;
 
 	old_regs = get_irq_regs();
-	this_cpu_write(irq_regs, new_regs);
+	__this_cpu_write(irq_regs, new_regs);
 
 	return old_regs;
 }