Fusion and RT Rreempt [Was: RTAI/fusion 0.7.2]

Gilles Chanteperdrix gilles.chanteperdrix at laposte.net
Thu Jun 2 01:53:29 CEST 2005

Max Krasnyansky wrote:
 > Yeah, but result from my app does not look very good, does it ?
 > I mean 36.8 usec from kernel task to user task. There is also about 5 usec
 > worst case interrupt dispatch latency (measured long time ago with oscope).
 > So the total is more than 40 usec to propagate interrupt into the user-space.
 > Remember when you and Paolo said that you're seeing 15 usec worst case
 > latency. I said that it's with the timer compensation and stuff, actual
 > interrupt response time is much worse.

Timer compensation is less than 10us. The rest of the difference
could conceivably come from the fact that the latency test has a 100us
period whereas your external interrupt is triggered every 4ms, which
would cause disastrous cache effect.

What happens if you run the latency test with a 4ms period?


					    Gilles Chanteperdrix.

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