Hi Brandon 1. I agree with jitter involved with processing interrupts and 100% cpu usage during polling for the same, so is there no way to let the user-space know that interrupt has occurred apart from polling ? 2. The reason why i said pseudo-interrupt is because we are polling and waiting there which is same as watching a flag in a UART register for RX flag to set. 3. I am curious as to how interrupts for Ethernet and usb are written. I am guessing that the ISR will use the DMA to transfer bytes to user-space. But even in that case the userspace should know that a new data has arrived. Then hoe to synchronize the kernel space and user-space if there are to share a data ?
Thanks... On Thursday, September 11, 2014 2:26:15 AM UTC+5:30, Brandon I wrote: > > > 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. > > On Wed, Sep 10, 2014 at 5:13 AM, neo <prag....@gmail.com <javascript:>> > 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.
