[Xen-devel] [PATCH 02/15] xen: tracing: avoid checking tb_init_done multiple times.

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

In fact, when calling __trace_var() directly, we can
assume that tb_init_done has been checked to be true,
and the if is hence redundant.

While there, also:
 - still in __trace_var(), move the check that the event
   is actually being traced up a little bit (to bail as
   soon as possible, if it is not);
 - make it explicit that tb_init_done is likely 0 in
   trace_will_trace_event(), as it is almost everywhere
   in the code.

Signed-off-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
---
Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
---
 xen/common/trace.c |    8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/xen/common/trace.c b/xen/common/trace.c
index 4fedc26..f29cd4c 100644
--- a/xen/common/trace.c
+++ b/xen/common/trace.c
@@ -311,7 +311,7 @@ static int tb_set_size(unsigned int pages)
 
 int trace_will_trace_event(u32 event)
 {
-    if ( !tb_init_done )
+    if ( likely(!tb_init_done) )
         return 0;
 
     /*
@@ -691,7 +691,8 @@ void __trace_var(u32 event, bool_t cycles, unsigned int 
extra,
     unsigned int extra_word;
     bool_t started_below_highwater;
 
-    if( !tb_init_done )
+    /* If the event is not interesting, bail, as early as possible */
+    if ( (tb_event_mask & event) == 0 )
         return;
 
     /* Convert byte count into word count, rounding up */
@@ -705,9 +706,6 @@ void __trace_var(u32 event, bool_t cycles, unsigned int 
extra,
     /* Round size up to nearest word */
     extra = extra_word * sizeof(u32);
 
-    if ( (tb_event_mask & event) == 0 )
-        return;
-
     /* match class */
     if ( ((tb_event_mask >> TRC_CLS_SHIFT) & (event >> TRC_CLS_SHIFT)) == 0 )
         return;


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