Messages in this thread | | | Date | Fri, 9 May 2003 11:37:29 +0000 | From | paubert <> | Subject | Re: how to measure scheduler latency on powerpc? realfeel doesn't work due to /dev/rtc issues |
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On Fri, May 09, 2003 at 02:14:13AM -0400, Chris Friesen wrote: > William Lee Irwin III wrote: > > >Try the timebase instead. > > The timestamp is not hard to get. The problem is getting a medium-frequency > > (2KHz or so) hardware interrupt to drive the test.
Reload the decrementer with a smaller value, and read the decrementer value at the beginning of every timer_interrupt. Timekeeping only depends on the timebase on PPC (I wrote most of the code), taking additional decrementer interrupts does not harm. Actually the simplest and most efficient way to perform a self IPI on PPC is to write 0 to the decrementer (2 machine instructions).
Actually, a way to measure the longest time during which interrupts are masked would be:
- when disabling interrupts, set decrementer to zero if they were previously enabled. - read the decrementer on every timer/external interrupt, if the value is negative and too large print the value and the point at which the interrupts were reenabled.
That's not perfect (it will generate not too many false positives but quite some overhead, but it should work).
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