POPF is a horribly expensive instruction, while STI is an optimised fastpath.
Switching POPF for a conditional branch and STI caused an 8% perf improvement
in various linux measurements. While I don't expect the change to be that
dramatic in Xen, there will be an improvement.
Furthermore, there is the following code generation improvement:
add/remove: 0/0 grow/shrink: 3/52 up/down: 52/-966 (-914)
owing to not needing to opencode the restriction to just IF in asm.
Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com>
---
CC: Jan Beulich <jbeul...@suse.com>
CC: Roger Pau Monné <roger....@citrix.com>
CC: Wei Liu <w...@xen.org>
---
xen/arch/x86/include/asm/system.h | 9 ++-------
1 file changed, 2 insertions(+), 7 deletions(-)
diff --git a/xen/arch/x86/include/asm/system.h
b/xen/arch/x86/include/asm/system.h
index 65e63de69a67..4be235472ecd 100644
--- a/xen/arch/x86/include/asm/system.h
+++ b/xen/arch/x86/include/asm/system.h
@@ -267,13 +267,8 @@ static inline unsigned long
array_index_mask_nospec(unsigned long index,
})
#define local_irq_restore(x) \
({ \
- BUILD_BUG_ON(sizeof(x) != sizeof(long)); \
- asm volatile ( "pushfq\n\t" \
- "andq %0, (%%rsp)\n\t" \
- "orq %1, (%%rsp)\n\t" \
- "popfq" \
- : : "i?r" ( ~X86_EFLAGS_IF ), \
- "ri" ( (x) & X86_EFLAGS_IF ) ); \
+ if ( (x) & X86_EFLAGS_IF ) \
+ local_irq_enable(); \
})
static inline int local_irq_is_enabled(void)
--
2.30.2
