On 06.12.2021 14:55, Andrew Cooper wrote: > On 06/12/2021 13:38, Andrew Cooper wrote: >> 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 <[email protected]> >> --- >> CC: Jan Beulich <[email protected]> >> CC: Roger Pau Monné <[email protected]> >> CC: Wei Liu <[email protected]> >> --- >> 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(); \ >> }) > > Bah. There's still the one total abuse of local_irq_restore() to > disable interrupts.
Question is whether that's really to be considered an abuse: To me "restore" doesn't mean only "maybe re-enable", but also "maybe re-disable". And a conditional STI-or-CLI is likely still be better than POPF. Jan
