On Fri, May 14, 2010 at 02:32:22PM +0200, Armin Steinhoff wrote: > > Do you see a use case which shows that a reasonably modern CPU has > > performance problems with SocketCAN, while it works fine with your > > userspace driver? My impression from previous projects is that, for > > all real life scenarios, the advantage of having a standard hardware > > abstraction in the kernel > > How many "hardware abstractions" do you want in the kernel? The kernel policy is to offer only one abstraction model for one sort of hardware; SocketCAN is a native Linux implementation and has no additional HAL. > The response time of the whole real-time application > (hardware/driver/application) is the point. If Linux wouldn't able to > handle every 100us a CAN frame ... the whole real-time application > would be useless. I still don't understand your setup, can you elaborate? > > Sending lots of frames works also if you have for example a CAN chip > > with a long FIFO, push the frames in and wait forever. > > But every so called "long FIFO" is limited and can reach the overun > state. My point is to find out where you see a relation to "latency". Latency has nothing to do with CAN frames per second. If you have a FIFO which is long enough, feeding it every let's say 1 second with 1k messages is enough to get 1k messages/s. So a system latency of 1 s would fulfill your throughput requirements. > > "Repsonse time" does involve some kind of round trip, which one do > > you mean? > > Responses of an real-time application to external events ... > > > Can you elaborate where you see the need for us response times? > > > > As the minimum reaction time is limited by hardware constraints on > > modern cpus anyway, I think that for most applications which require > > sub 100 us response times, a hardware solution (microcontroller, > > fpga) is a better way to achive things. > > Why should we use FPGAs when a CPU has multiple cores? Every fast > fieldbus (e.g. EtherCAT) needs a reaction time with less than 100us. Reaction time between *which events*? Sorry, I didn't understand your use case yet. Thanks, rsc -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
