The program that captures data is the messenger between the instrumented kernel and the filesystem.
Figure 1Possible data capture configurations.
The main function of the data-capture program is to send the buffers given
to it by the instrumented kernel to an output device or a file.
To accomplish this function, the program must also:
interface with the kernel
specify data-filtering requirements the kernel will use
You must configure the instrumented kernel before logging.
The kernel configuration settings include:
buffer allocations (size)
which events and classes of events to log (filtering)
whether to log the events in wide mode or fast mode
Note:
The kernel retains the settings, and multiple programs access a single kernel configuration.
Changing the settings in one process supercedes the settings made in another.
We've provided
tracelogger
as the default data-capture utility.
Although you can write your own utility, there's little need to.
You can control the capture of data via
qconn
(under the control of the Integrated Development Environment, or IDE),
tracelogger
(from the command line), or directly from your application.
All three approaches use the
TraceEvent()
function to control the kernel:
Figure 2Controlling the capture of trace data.
For information about controlling the trace from the IDE, see the
Analyzing System Behavior chapter of the IDE User's Guide.
Let's look first at using tracelogger, and then
we'll describe how you can use TraceEvent() to control tracing
from your application.
CAUTION:
Don't run more than one instance of tracelogger at a time.
Similarly, don't run tracelogger and trace events under control of the IDE at the same time.
The hardware underlying ClockCycles()
must be synchronized across all processors on an SMP system.
If the clocks aren't synchronized, then tracelogger produces
data with inconsistent timestamps, and the IDE won't be able to load the trace file.
The IDE attempts to properly order the events in
the trace file, and this can go awry if the timestamp data is incorrect.
The traceprinter utility doesn't have any issues with such
traces because it doesn't attempt to reorder and then interpret the data;
it simply dumps the contents of each event.
