Messages in this thread | | | Date | Thu, 8 May 2003 20:56:29 -0400 (EDT) | From | "Richard B. Johnson" <> | Subject | Re: how to measure scheduler latency on powerpc? realfeel doesn't work due to /dev/rtc issues |
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On Thu, 8 May 2003, William Lee Irwin III wrote:
> On Thu, May 08, 2003 at 06:12:12PM -0400, Chris Friesen wrote: > >>> I'm trying to test the scheduler latency on a powerpc platform. It appears > >>> that a realfeel type of program won't work since you can't program /dev/rtc > >>> to generated interrupts on powerpc. Is there anything similar which could > >>> be done? > > On Thu, 8 May 2003, William Lee Irwin III wrote: > > > Why would you want to use an interrupt? Just count jiffies in sched.c > > On Thu, May 08, 2003 at 05:38:23PM -0700, Davide Libenzi wrote: > > I don't know what he does mean for scheduler latency, but if it is the ctx > > switch one something like get_cycles() will be better instead of jiffies. > > True, if you're looking for performance tweaks and not pathologies (which > I was) you'll need something that accurate. > > > -- wli Does it have a printer port like the Intel machines? If so, set it up to generate interrupts on the 'event' pin (paper-out, etc.) and have the ISR parrot the status bits out the printer-port bits.
Start it up and put function generator on the event bit. measure the delay beteen that bin and the data data bit(s) with a 'scope. This tells you the whole story, the total time necessary for an ISR to actually do something.
Cheers, Dick Johnson Penguin : Linux version 2.4.20 on an i686 machine (797.90 BogoMips). Why is the government concerned about the lunatic fringe? Think about it.
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