[PATCH] x86-64: improve insn scheduling in SAVE_ARGS_IRQ

[Jan Beulich]

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@xxxxxxxx>

---
 arch/x86/kernel/entry_64.S |    7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

--- 3.2-rc3/arch/x86/kernel/entry_64.S
+++ 3.2-rc3-x86_64-entry-sched/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, \



--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/