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[PATCH] x86/irq: Improve local_irq_restore() code generation and performance
- To: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Mon, 6 Dec 2021 13:38:28 +0000
- Authentication-results: esa1.hc3370-68.iphmx.com; dkim=none (message not signed) header.i=none
- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>
- Delivery-date: Mon, 06 Dec 2021 13:38:54 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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.
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
---
xen/include/asm-x86/system.h | 9 ++-------
1 file changed, 2 insertions(+), 7 deletions(-)
diff --git a/xen/include/asm-x86/system.h b/xen/include/asm-x86/system.h
index 65e63de69a67..4be235472ecd 100644
--- a/xen/include/asm-x86/system.h
+++ b/xen/include/asm-x86/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)
--
2.11.0
|
