Difference between revisions of "RTWG-discussion-points"
From eLinux.org
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* 2-machine system gives unbiased timing results | * 2-machine system gives unbiased timing results | ||
** instrumentation does not interfere with the timings | ** 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 | ||
Revision as of 02:03, 4 September 2007
Contents |
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
