From: Brandon I <brandon.ir...@gmail.com> Reply-To: "beagleboard@googlegroups.com" <beagleboard@googlegroups.com> Date: Wednesday, September 10, 2014 at 1:55 PM To: "beagleboard@googlegroups.com" <beagleboard@googlegroups.com> Subject: Re: [beagleboard] Re: registering asynchronous events on kernel thread in user space
>> > pseudo-interrupt from user space > > There's nothing pseudo about it. Again, any usual way to have a userspace > application respond to an interrupt will be the exact same. The kernel will > block the userspace process until the interrupt is seen. The only real > alternative is burning up the cpu with memory polling, which appears to be > what the BBIOlib method uses. So, your latency is limited to your poll speed > (which can be faster than interrupts). But, if you have a constant poll for > minimum latency, lets hope you're not trying to do something important > elsewhere since your cpu usage will be at 100%, and you'll be maximizing > process to process context switching! > > For 4, The only difference between a userspace and kernel space interrupt > handler is where the code is that responds to the interrupt. You will only > benefit from writing your own interrupt handler if you put all of your code > that does something with that interrupt in the kernel. Otherwise, you're back > to process blocked by kernel, interrupt occurs, kernel unblocks process, > process does something after seeing the interrupt....back to the sysfs/UIO > method. > > I would try some benchmarks. See if the regular UIO/sysfs interrupt method > gives you sufficient performance. And definitely keep in mind John's > statement. You're going to see a massive amount of jitter for anything in > userspace or kernel space (better jitter since you can disable interrupts and > whatnot, but if you don't finish quickly in kernel space, you'll crash the > kernel). > > If something like a precise timestamp is needed for an async event, then there > are other ways to approach this. If you're looking for fixed low latency, > you're doomed. I agree with everything Brandon just articulated. Regards, John > > On Wed, Sep 10, 2014 at 5:13 AM, neo <prag.in...@gmail.com> wrote: >> pseudo-interrupt from user space > > > > -- > For more options, visit http://beagleboard.org/discuss > --- > You received this message because you are subscribed to the Google Groups > "BeagleBoard" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to beagleboard+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to beagleboard+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
