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authorJesper Dangaard Brouer <[email protected]>2017-08-22 19:22:43 +0200
committerIngo Molnar <[email protected]>2017-08-25 11:04:18 +0200
commitd0618410eced4eb092295fad10312a4545fcdfaf (patch)
tree927f02a812f22f476c608dabcd4e6b25917963ff
parent1d953111b648e48923171c3c9cf17be2250544fa (diff)
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 <[email protected]> Signed-off-by: Peter Zijlstra (Intel) <[email protected]> Cc: Arnaldo Carvalho de Melo <[email protected]> Cc: Jiri Olsa <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Thomas Gleixner <[email protected]> Link: http://lkml.kernel.org/r/150342256382.16595.986861478681783732.stgit@firesoul Signed-off-by: Ingo Molnar <[email protected]>
-rw-r--r--kernel/events/internal.h2
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/events/internal.h b/kernel/events/internal.h
index 5377c591c57a..843e97047335 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;