In an XDP redirect applications using tracepoint xdp:xdp_redirect to diagnose TX overrun, I noticed perf_swevent_get_recursion_context() was consuming 2% CPU. This was reduced to 1.6% with this simple change.
Looking at the annotated asm code, it was clear that the unlikely case in_nmi() test was chosen (by the compiler) as the most likely event/branch. This small adjustment makes the compiler (gcc version 7.1.1 20170622 (Red Hat 7.1.1-3)) put in_nmi() as an unlikely branch. Signed-off-by: Jesper Dangaard Brouer <bro...@redhat.com> --- kernel/events/internal.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/events/internal.h b/kernel/events/internal.h index 486fd78eb8d5..56aa462760fa 100644 --- a/kernel/events/internal.h +++ b/kernel/events/internal.h @@ -208,12 +208,12 @@ static inline int get_recursion_context(int *recursion) { int rctx; - if (in_nmi()) - rctx = 3; + if (in_softirq()) + rctx = 1; else if (in_irq()) rctx = 2; - else if (in_softirq()) - rctx = 1; + else if (in_nmi()) + rctx = 3; else rctx = 0;