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mb() typically uses mfence on modern x86, but a micro-benchmark shows that it's 2 to 3 times slower than lock; addl $0,(%%e/rsp) that we use on older CPUs. So let's use the locked variant everywhere - helps keep the code simple as well. While I was at it, I found some inconsistencies in comments in arch/x86/include/asm/barrier.h I hope I'm not splitting this up too much - the reason

mb() typically uses mfence on modern x86, but a micro-benchmark shows that it's 2 to 3 times slower than lock; addl $0,(%%e/rsp) that we use on older CPUs. So let's use the locked variant everywhere - helps keep the code simple as well. While I was at it, I found some inconsistencies in comments in arch/x86/include/asm/barrier.h I hope I'm not splitting this up too much - the reason

...because of weird use-cases e.g. dealing with WC memory. Drop this comment. Signed-off-by: Michael S. Tsirkin <mst at redhat.com> --- arch/x86/include/asm/barrier.h | 5 ----- 1 file changed, 5 deletions(-) diff --git a/arch/x86/include/asm/barrier.h b/arch/x86/include/asm/barrier.h index 7f99726..eb220b8 100644 --- a/arch/x86/include/asm/barrier.h +++ b/arch/x86/include/asm/barrier.h @@ -11,11 +11,6 @@ */ #ifdef CONFIG_X86_32 -/* - * Some non-Intel clones support out of order store. wmb() ceases to be a - * nop for these. - */ - #define mb() asm volatile("lock; addl $0,0(%%esp)&...