linux-kernel - [tip:x86/asm] x86-64: Improve insn scheduling in SAVE_ARGS

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Date:	Fri, 24 Feb 2012 12:17:38 -0800
From:	tip-bot for Jan Beulich <JBeulich@...e.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
	jbeulich@...e.com, JBeulich@...e.com, ak@...ux.intel.com,
	tglx@...utronix.de, hpa@...ux.intel.com
Subject: [tip:x86/asm] x86-64: Improve insn scheduling in SAVE_ARGS_IRQ

Commit-ID:  69466466ce889cd2cbc8cda9ff1c6083f48cc7f9
Gitweb:     http://git.kernel.org/tip/69466466ce889cd2cbc8cda9ff1c6083f48cc7f9
Author:     Jan Beulich <JBeulich@...e.com>
AuthorDate: Fri, 24 Feb 2012 11:55:01 +0000
Committer:  H. Peter Anvin <hpa@...ux.intel.com>
CommitDate: Fri, 24 Feb 2012 11:46:28 -0800

x86-64: Improve insn scheduling in SAVE_ARGS_IRQ

In one case, use an address register that was computed earlier (and
with a simpler instruction), thus reducing the risk of a stall.

In the second case, eliminate a branch by using a conditional move (as
is already done in call_softirq and xen_do_hypervisor_callback).

Signed-off-by: Jan Beulich <jbeulich@...e.com>
Link: http://lkml.kernel.org/r/4F4788A50200007800074A26@nat28.tlf.novell.com
Reviewed-by: Andi Kleen <ak@...ux.intel.com>
Signed-off-by: H. Peter Anvin <hpa@...ux.intel.com>
---
 arch/x86/kernel/entry_64.S |    7 +++----
 1 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index a20e1cb..211b2e1 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -319,7 +319,7 @@ ENDPROC(native_usergs_sysret64)
 	movq %rsp, %rsi
 
 	leaq -RBP(%rsp),%rdi	/* arg1 for handler */
-	testl $3, CS(%rdi)
+	testl $3, CS-RBP(%rsi)
 	je 1f
 	SWAPGS
 	/*
@@ -329,11 +329,10 @@ ENDPROC(native_usergs_sysret64)
 	 * moving irq_enter into assembly, which would be too much work)
 	 */
 1:	incl PER_CPU_VAR(irq_count)
-	jne 2f
-	mov PER_CPU_VAR(irq_stack_ptr),%rsp
+	cmovzq PER_CPU_VAR(irq_stack_ptr),%rsp
 	CFI_DEF_CFA_REGISTER	rsi
 
-2:	/* Store previous stack value */
+	/* Store previous stack value */
 	pushq %rsi
 	CFI_ESCAPE	0x0f /* DW_CFA_def_cfa_expression */, 6, \
 			0x77 /* DW_OP_breg7 */, 0, \
--
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