The PerfMeasurement.jsm
JavaScript code module lets you take detailed performance measurements of your code.
PerfMeasurement.jsm
JavaScript code module can only be used from chrome -- that is, from within the application itself or an add-on.Before you can use this module, you need to import it into your scope:
Components.utils.import("resource://gre/modules/PerfMeasurement.jsm")
See Measuring performance using the PerfMeasurement.jsm code module for details on how to use this API.
PerfMeasurement.jsm
is only functional on Linux, but it is planned to add support for Windows (bug 583322) and OSX (bug 583323) as well, and we welcome patches for other operating systems.Method overview
static bool canMeasureSomething(); |
void reset(); |
void start(); |
void stop(); |
Member fields
Recorded data variables
These variables provide access to the recorded data. Any measurable event that was not being recorded has a value of -1 (that is, 0xFFFFFFFFFFFFFFFF).
PerfMeasurement
object, then they are not zeroed again unless you explicitly call the reset()
method. This lets you accumulate measurements over multiple passes through code that you want to analyze.Variable | Type | Description |
cpu_cycles | uint64 | The number of CPU cycles elapsed. |
instructions | uint64 | The number of instructions executed. |
cache_references | uint64 | The number of memory accesses that occurred. |
cache_misses | uint64 | The number of times memory accesses missed the cache. |
branch_instructions | uint64 | The number of branch instructions executed. |
branch_misses | uint64 | The number of times branch prediction guessed wrong. |
bus_cycles | uint64 | The number of memory bus cycles that elapsed. |
page_faults | uint64 | The number of page exceptions the OS handled. |
major_page_faults | uint64 | The number of times page faults required disk access. |
context_switches | uint64 | The number of context switches that occurred involving the thread being profiled. |
cpu_migrations | uint64 | The number of times the profiled thread migrated from one CPU core to another. |
Event types measured constant
The eventsMeasured
constant provides a mask indicating which event types were recorded.
Variable | Type | Description |
eventsMeasured | EventMask | A bit mask of the event types recorded; this can differ from the events requested if the platform doesn't support all of the event types you specified when creating the PerfMeasurement object. |
Constants
Event mask constants
These constants are used to construct the mask indicating which events you want to monitor.
Constant | Value | Description |
CPU_CYCLES | 0x00000001 | Measure CPU cycles elapsed. |
INSTRUCTIONS | 0x00000002 | Measure the number of instructions executed. |
CACHE_REFERENCES | 0x00000004 | Measure the number of cache references. |
CACHE_MISSES | 0x00000008 | Measure the number of cache misses. |
BRANCH_INSTRUCTIONS | 0x00000010 | Measure the number of branch instructions executed. |
BRANCH_MISSES | 0x00000020 | Measure the number of times branch prediction guesses wrong. |
BUS_CYCLES | 0x00000040 | Measure the number of bus cycles elapsed. |
PAGE_FAULTS | 0x00000080 | Measure the number of page faults that occurred. |
MAJOR_PAGE_FAULTS | 0x00000100 | Measure the number of major page faults that occurred. |
CONTEXT_SWITCHES | 0x00000200 | Measure the number of context switches that occurred. |
CPU_MIGRATIONS | 0x00000400 | Measure the number of context switches that occurred. |
ALL | 0x000007FF | Measure all available events. |
Number of available event types
The NUM_MEASURABLE_EVENTS
constant tells you how many types of events can be measured.
Constant | Value | Description |
NUM_MEASURABLE_EVENTS | 11 | The number of types of events that can be measured. |
Constructor
Creates a new PerfMeasurement
object, configured to record the specified event types.
PerfMeasurement( EventMask toMeasure );
Parameters
toMeasure
- A mask of all of the event types you want to record; see Event mask constants for a list of values. OR together all the event types you want to record, and pass that value here. Pass
PerfMeasurement.ALL
to record all event types.
Return value
A new PerfMeasurement
object configured to record the specified event types.
Methods
canMeasureSomething()
Indicates whether or not the platform on which your code is running supports this code module.
static bool canMeasureSomething();
Parameters
None.
Return value
If even one of the event types can be recorded, this will return true
. Otherwise, it returns false
.
reset()
Resets all the enabled counters to zero.
void reset();
Parameters
None.
start()
Starts measuring the performance indicators that were specified when the PerfMeasurement
object was created.
void start();
Parameters
None.
stop()
Stops measuring performance data. For each enabled counter, the number of measured events of that type that occurred are added to the appropriate visible variable.
void stop();
Parameters
None.