RTWG-discussion-points

Review of test programs

lpptest

problems:

• requires 2 machines
• requires parallel port (not many embedded boards have this)
• uses TSC, which is i386-specific

benefits:

• built into the rt-preempt patch
• 2-machine system gives unbiased timing results
  • instrumentation does not interfere with the timings

realfeel

benefits:

• is one-machine
• uses /dev/rtc, does not use timer interrupt
  • this isolates the ISR handling from timer operations
• is a very simple test

problems:

• uses TSC, which is i386-specific
• doesn't have an instrumentation point in the kernel
  • no measurement of int latency, only process start latency
• process start latency is "guessed" from expected interrupt time
  • that is, it is not actually measured
• not all boards have a working /dev/rtc driver

igel test

This tests scheduling latency on receipt of a character on an SM501 uart. The UART driver gets a timestamp on ISR start, and can be asked for them from user-space after a run. The user-space driver measures the time from ISR start to task start. Test is specific to SH architecture. Uses SH hardware timer.

See http://tree.celinuxforum.org/CelfPubWiki/UserLevelDeviceDriver (page is in Japanese)

• Yung Joon will ask Takao Ikoma to translate this page.
• Matsubara-san will update the driver and some of the text on the page.
  • will attach latest driver source
• Tim will provide Ikoma-san e-mail