diff options
| -rw-r--r-- | docs/tracing.txt | 46 | ||||
| -rwxr-xr-x | scripts/tracetool | 9 |
2 files changed, 48 insertions, 7 deletions
diff --git a/docs/tracing.txt b/docs/tracing.txt index ea29f2c222..a92716f319 100644 --- a/docs/tracing.txt +++ b/docs/tracing.txt @@ -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 @@ -234,3 +228,43 @@ 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; + } diff --git a/scripts/tracetool b/scripts/tracetool index 4c9951d0aa..701b517ec1 100755 --- a/scripts/tracetool +++ b/scripts/tracetool @@ -519,7 +519,7 @@ linetostap_end_dtrace() # Process stdin by calling begin, line, and end functions for the backend convert() { - local begin process_line end str disable + local begin process_line end str name NAME enabled begin="lineto$1_begin_$backend" process_line="lineto$1_$backend" end="lineto$1_end_$backend" @@ -534,8 +534,15 @@ convert() # Process the line. The nop backend handles disabled lines. if has_property "$str" "disable"; then "lineto$1_nop" "$str" + enabled=0 else "$process_line" "$str" + enabled=1 + fi + if [ "$1" = "h" ]; then + name=$(get_name "$str") + NAME=$(echo $name | tr '[:lower:]' '[:upper:]') + echo "#define TRACE_${NAME}_ENABLED ${enabled}" fi done |