Commit-ID: d0618410eced4eb092295fad10312a4545fcdfaf Gitweb: http://git.kernel.org/tip/d0618410eced4eb092295fad10312a4545fcdfaf Author: Jesper Dangaard Brouer <bro...@redhat.com> AuthorDate: Tue, 22 Aug 2017 19:22:43 +0200 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Fri, 25 Aug 2017 11:04:18 +0200
tracing, perf: Adjust code layout in get_recursion_context() 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 1.85% 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> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> Cc: Arnaldo Carvalho de Melo <a...@kernel.org> Cc: Jiri Olsa <jo...@kernel.org> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Thomas Gleixner <t...@linutronix.de> Link: http://lkml.kernel.org/r/150342256382.16595.986861478681783732.stgit@firesoul Signed-off-by: Ingo Molnar <mi...@kernel.org> --- kernel/events/internal.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/events/internal.h b/kernel/events/internal.h index 5377c59..843e970 100644 --- a/kernel/events/internal.h +++ b/kernel/events/internal.h @@ -208,7 +208,7 @@ static inline int get_recursion_context(int *recursion) { int rctx; - if (in_nmi()) + if (unlikely(in_nmi())) rctx = 3; else if (in_irq()) rctx = 2;
