3. Data acquisition
3.1 Probing the kernel
Mount the relay filesystem.
Reboot and use the kernel built in the previous section. The rest of
these instructions assume you are logged in as root on the machine
with the patched kernel running. (This is the target machine if
you are using a host/target configuration.)
If it does not already exist, create a directory to mount the
relay filesystem in.
mount -t relayfs nodev /mnt/relay
Having done this, you should see a new entry in /proc/mounts.
3.2 Probing RTAI
You can now install the other RTAI modules and trace your system.
3.3 Recording the data
A trace begins when the trace daemon tells the
kernel to start recording events. To start recording, do:
tracedaemon -tsT./out.trace ./out.proc
out.trace will contain the raw events and out.proc will contain
data read from /proc that will enable the decoder to know the process'
name and hierarchy. Replace T by the number of seconds you want the
daemon to run. Using the given command line, the out.trace file will use,
approximatively, 30 M per minute it runs for a heavy loaded system. On
a normal workstation without X, the usage is less than 1 M per minute. It
is possible to reduce the usage by choosing not to trace certain events. See
the following section for the daemon's command-line options.
If you didn't specify the -t option, then you must stop the trace daemon
manually. For normal trace mode, do this by sending it a TERM signal.
using the kill command. First, use ps to find
out the process ID of the tracedaemon. Then use this PID with the
kill [daemon pid]
Since the daemon and the decoder are often used in the same way on multiple runs, it is
desirable to write simple scripts to automate the passing of options. The last
section, of this Help, documents some scripts already available.