lkml.org 
[lkml]   [2017]   [Aug]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Subject[PATCH] trace: adjust code layout in get_recursion_context
From
Date
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 <brouer@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;

\
 
 \ /
  Last update: 2017-08-22 16:41    [W:0.064 / U:1.336 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site