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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@suse.com>
AuthorDate: Fri, 24 Feb 2012 11:55:01 +0000
Committer: H. Peter Anvin <hpa@linux.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@suse.com>
Link: http://lkml.kernel.org/r/4F4788A50200007800074A26@nat28.tlf.novell.com
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.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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