@@ -39,12 +39,12 @@ generate code for the trace events. Trace events are invoked directly from
source code like this:
#include "trace.h" /* needed for trace event prototype */
-
+
void *qemu_vmalloc(size_t size)
{
void *ptr;
size_t align = QEMU_VMALLOC_ALIGN;
-
+
if (size < align) {
align = getpagesize();
}
@@ -98,12 +98,6 @@ respectively. This ensures portability between 32- and 64-bit platforms.
4. Name trace events after their function. If there are multiple trace events
in one function, append a unique distinguisher at the end of the name.
-5. If specific trace events are going to be called a huge number of times, this
- might have a noticeable performance impact even when the trace events are
- programmatically disabled. In this case you should declare the trace event
- with the "disable" property, which will effectively disable it at compile
- time (using the "nop" backend).
-
== Generic interface and monitor commands ==
You can programmatically query and control the dynamic state of trace events
@@ -227,3 +221,43 @@ probes:
--target-type system \
--target-arch x86_64 \
<trace-events >qemu.stp
+
+== Trace event properties ==
+
+Each event in the "trace-events" file can be prefixed with a space-separated
+list of zero or more of the following event properties.
+
+=== "disable" ===
+
+If a specific trace event is going to be invoked a huge number of times, this
+might have a noticeable performance impact even when the event is
+programmatically disabled.
+
+In this case you should declare such event with the "disable" property. This
+will effectively disable the event at compile time (by using the "nop" backend),
+thus having no performance impact at all on regular builds (i.e., unless you
+edit the "trace-events" file).
+
+In addition, there might be cases where relatively complex computations must be
+performed to generate values that are only used as arguments for a trace
+function. In these cases you can use the macro 'TRACE_${EVENT_NAME}_ENABLED' to
+guard such computations and avoid its compilation when the event is disabled:
+
+ #include "trace.h" /* needed for trace event prototype */
+
+ void *qemu_vmalloc(size_t size)
+ {
+ void *ptr;
+ size_t align = QEMU_VMALLOC_ALIGN;
+
+ if (size < align) {
+ align = getpagesize();
+ }
+ ptr = qemu_memalign(align, size);
+ if (TRACE_QEMU_VMALLOC_ENABLED) { /* preprocessor macro */
+ void *complex;
+ /* some complex computations to produce the 'complex' value */
+ trace_qemu_vmalloc(size, ptr, complex);
+ }
+ return ptr;
+ }
@@ -123,6 +123,13 @@ def trace_h_begin(events):
@for_format("h", END)
def trace_h_end(events):
+ for e in events:
+ if 'disable' in e.properties:
+ enabled = 0
+ else:
+ enabled = 1
+ print "#define TRACE_%s_ENABLED %d" % (e.name.upper(), enabled)
+ print
print '#endif /* TRACE_H */'