Messages in this thread | | | Date | Mon, 13 Jun 2005 17:00:21 +0200 | From | Ingo Molnar <> | Subject | Re: PREEMPT_RT vs ADEOS: the numbers, part 1 |
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* Karim Yaghmour <karim@opersys.com> wrote:
> Ingo Molnar wrote: > > how were interrupt response times measured, precisely? What did the > > target (measured) system have to do to respond to an interrupt? Did you > > use the RTC to measure IRQ latencies? > > The logger used two TSC values. One prior to shooting the interrupt to > the target, and one when receiving the response. Responding to an > interrupt meant that a driver was hooked to the target's parallel port > interrupt and simply acted by toggling an output pin on the parallel > port, which in turn was hooked onto the logger's parallel port in a > similar fashion. [...]
FYI, there's a new feature in the -V0.7.48-25 (and later) -RT patches that implements this: CONFIG_LPPTEST. It is a simple standalone driver and userspace utility from Thomas Gleixner that can be used to measure the IRQ-latency of the system over a null-modem-parallel-cable.
to use it, enable CONFIG_LPPEST in the .config [disable CONFIG_PARPORT first], boot the kernel on both the target and the host systems, and then run the scripts/testlpp utility on the host system which will measure latencies and will do a maximum-search.
(the driver assumes normal LPT1 PC layout - 0x378/IRQ7)
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