[PATCH v1 1/3] x86/entry: Test ti_work for zero before processing individual bits
From: Xin Li (Intel)
Date: Wed Aug 07 2024 - 01:50:53 EST
In most cases, ti_work values passed to arch_exit_to_user_mode_prepare()
are zeros, e.g., 99% in kernel build tests. So an obvious optimization
is to test ti_work for zero before processing individual bits in it.
In addition, Intel 0day tests find no perf regression with this change.
Suggested-by: H. Peter Anvin (Intel) <hpa@xxxxxxxxx>
Signed-off-by: Xin Li (Intel) <xin@xxxxxxxxx>
---
arch/x86/include/asm/entry-common.h | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)
diff --git a/arch/x86/include/asm/entry-common.h b/arch/x86/include/asm/entry-common.h
index fb2809b20b0a..4c78b99060b5 100644
--- a/arch/x86/include/asm/entry-common.h
+++ b/arch/x86/include/asm/entry-common.h
@@ -47,15 +47,17 @@ static __always_inline void arch_enter_from_user_mode(struct pt_regs *regs)
static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,
unsigned long ti_work)
{
- if (ti_work & _TIF_USER_RETURN_NOTIFY)
- fire_user_return_notifiers();
+ if (unlikely(ti_work)) {
+ if (ti_work & _TIF_USER_RETURN_NOTIFY)
+ fire_user_return_notifiers();
- if (unlikely(ti_work & _TIF_IO_BITMAP))
- tss_update_io_bitmap();
+ if (unlikely(ti_work & _TIF_IO_BITMAP))
+ tss_update_io_bitmap();
- fpregs_assert_state_consistent();
- if (unlikely(ti_work & _TIF_NEED_FPU_LOAD))
- switch_fpu_return();
+ fpregs_assert_state_consistent();
+ if (unlikely(ti_work & _TIF_NEED_FPU_LOAD))
+ switch_fpu_return();
+ }
#ifdef CONFIG_COMPAT
/*
--
2.45.2