linux-kernel - [RFC 29/30] x86/entry: Force inlining of 32-bit syscall code

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Message-Id: <3c6ceff654f1df8552f5d8e442475e5eec56aa7c.1441146105.git.luto@kernel.org>
Date:	Tue,  1 Sep 2015 15:41:29 -0700
From:	Andy Lutomirski <luto@...nel.org>
To:	x86@...nel.org, linux-kernel@...r.kernel.org
Cc:	Brian Gerst <brgerst@...il.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Andy Lutomirski <luto@...nel.org>
Subject: [RFC 29/30] x86/entry: Force inlining of 32-bit syscall code

On systems that support fast syscalls, we only really care about the
performance of the fast syscall path.  Forcibly inline it and add
a likely annotation.

This saves 4-6 cycles.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/entry/common.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index 0fa55f0736f6..a3c4e7aa573b 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -324,9 +324,11 @@ __visible void syscall_return_slowpath(struct pt_regs *regs)
 #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
 /*
  * Does a 32-bit syscall.  Called with IRQs on and does all entry and
- * exit work and returns with IRQs off.
+ * exit work and returns with IRQs off.  This function is extremely hot
+ * in workloads that use it, and it's usually called from
+ * do_fast_syscall_32, so forcibly inline it to improve performance.
  */
-static void do_syscall_32_irqs_on(struct pt_regs *regs)
+static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)
 {
 	struct thread_info *ti = pt_regs_to_thread_info(regs);
 	unsigned int nr = (unsigned int)regs->orig_ax;
@@ -345,7 +347,7 @@ static void do_syscall_32_irqs_on(struct pt_regs *regs)
 		nr = syscall_trace_enter(regs);
 	}
 
-	if (nr < IA32_NR_syscalls) {
+	if (likely(nr < IA32_NR_syscalls)) {
 		/*
 		 * It's possible that a 32-bit syscall implementation
 		 * takes a 64-bit parameter but nonetheless assumes that
-- 
2.4.3

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