linux-kernel - [PATCH v2 4/5] x86/fpu: Speed up lazy FPU restores slightly

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Message-Id: <980004297e233c27066d54e71382c44cdd36ef7c.1453675014.git.luto@kernel.org>
Date:	Sun, 24 Jan 2016 14:38:09 -0800
From:	Andy Lutomirski <luto@...nel.org>
To:	x86@...nel.org, linux-kernel@...r.kernel.org
Cc:	Borislav Petkov <bp@...en8.de>, Fenghua Yu <fenghua.yu@...el.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>,
	yu-cheng yu <yu-cheng.yu@...el.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>
Subject: [PATCH v2 4/5] x86/fpu: Speed up lazy FPU restores slightly

If we have an FPU, there's no need to check CR0 for FPU emulation.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/kernel/traps.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 87f80febf477..36a9c017540e 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -752,7 +752,7 @@ do_device_not_available(struct pt_regs *regs, long error_code)
 	RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
 
 #ifdef CONFIG_MATH_EMULATION
-	if (read_cr0() & X86_CR0_EM) {
+	if (!boot_cpu_has(X86_FEATURE_FPU) && (read_cr0() & X86_CR0_EM)) {
 		struct math_emu_info info = { };
 
 		conditional_sti(regs);
-- 
2.5.0