[Xen-devel] [PATCH 1 of 3] xentrace: Skip to low cpu when throwing away portions of the circular buffer

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

Skip to the next "low" cpu when throwing away portions of the circular
memory buffer.  This makes subsequent analysis easier.

Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>

diff -r 859a372efa66 -r 16ef34de0129 tools/xentrace/xentrace.c
--- a/tools/xentrace/xentrace.c Tue Apr 13 13:40:58 2010 +0100
+++ b/tools/xentrace/xentrace.c Tue Apr 13 17:24:07 2010 +0100
@@ -149,6 +149,7 @@
 {
     struct cpu_change_record *rec;
     long need_to_consume, free, freed;
+    int last_cpu = -1;
 
     if ( membuf.pending_size > 0 )
     {
@@ -193,11 +194,25 @@
 
         if ( need_to_consume > 0 )
         {
+            last_cpu = rec->data.cpu;
             MEMBUF_CONS_INCREMENT(freed);
             need_to_consume -= freed;
         }
     } while( need_to_consume > 0 );
 
+    /* For good tsc consistency, we need to start at a low-cpu buffer.  Keep
+     * skipping until the cpu goes down or stays the same. */
+    rec = (struct cpu_change_record *)MEMBUF_POINTER(membuf.cons);
+    while ( rec->data.cpu > last_cpu )
+    {
+        last_cpu = rec->data.cpu; 
+
+        freed = sizeof(*rec) + rec->data.window_size;
+        
+        MEMBUF_CONS_INCREMENT(freed);
+        rec = (struct cpu_change_record *)MEMBUF_POINTER(membuf.cons);
+    }
+
 start_window:
     /*
      * Start writing "pending" data.  Update prod once all this data is

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