[Xen-changelog] [xen-unstable] [XENTRACE] Remember number of lost trace records when

[Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User kfraser@xxxxxxxxxxxxxxxxxxxxx
# Node ID e05d60be5adb22afc42d18d631041cc6e2ccbe91
# Parent  3cdb93867f817243f6e770baf72c58a40d33de5c
[XENTRACE] Remember number of lost trace records when
trace buffer is full and write a 'number of lost records'
entry when space becomes available.
From: Rob Gardner <rob.gardner@xxxxxx>
Signed-off-by: Keir Fraser <keir@xxxxxxxxxxxxx>
---
 xen/common/trace.c         |   23 ++++++++++++++++++++---
 xen/include/public/trace.h |    1 +
 2 files changed, 21 insertions(+), 3 deletions(-)

diff -r 3cdb93867f81 -r e05d60be5adb xen/common/trace.c
--- a/xen/common/trace.c        Mon Jul 10 16:09:20 2006 +0100
+++ b/xen/common/trace.c        Mon Jul 10 17:05:44 2006 +0100
@@ -46,6 +46,8 @@ static int nr_recs;
 /* Send virtual interrupt when buffer level reaches this point */
 static int t_buf_highwater;
 
+/* Number of records lost due to per-CPU trace buffer being full. */
+static DEFINE_PER_CPU(unsigned long, lost_records);
 
 /* a flag recording whether initialization has been done */
 /* or more properly, if the tbuf subsystem is enabled right now */
@@ -234,7 +236,7 @@ void trace(u32 event, unsigned long d1, 
     struct t_buf *buf;
     struct t_rec *rec;
     unsigned long flags;
-
+    
     BUG_ON(!tb_init_done);
 
     if ( (tb_event_mask & event) == 0 )
@@ -259,10 +261,25 @@ void trace(u32 event, unsigned long d1, 
 
     local_irq_save(flags);
 
-    if ( (buf->prod - buf->cons) >= nr_recs )
-    {
+    /* Check if space for two records (we write two if there are lost recs). */
+    if ( (buf->prod - buf->cons) >= (nr_recs - 1) )
+    {
+        this_cpu(lost_records)++;
         local_irq_restore(flags);
         return;
+    }
+
+    if ( unlikely(this_cpu(lost_records) != 0) )
+    {
+        rec = &t_recs[smp_processor_id()][buf->prod % nr_recs];
+        memset(rec, 0, sizeof(*rec));
+        rec->cycles  = (u64)get_cycles();
+        rec->event   = TRC_LOST_RECORDS;
+        rec->data[0] = this_cpu(lost_records);
+        this_cpu(lost_records) = 0;
+
+        wmb();
+        buf->prod++;
     }
 
     rec = &t_recs[smp_processor_id()][buf->prod % nr_recs];
diff -r 3cdb93867f81 -r e05d60be5adb xen/include/public/trace.h
--- a/xen/include/public/trace.h        Mon Jul 10 16:09:20 2006 +0100
+++ b/xen/include/public/trace.h        Mon Jul 10 17:05:44 2006 +0100
@@ -26,6 +26,7 @@
 #define TRC_VMXIO    0x00088000   /* VMX io emulation trace  */
 
 /* Trace events per class */
+#define TRC_LOST_RECORDS        (TRC_GEN + 1)
 
 #define TRC_SCHED_DOM_ADD       (TRC_SCHED +  1)
 #define TRC_SCHED_DOM_REM       (TRC_SCHED +  2)

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