Hi, On Thu, Mar 28, 2013 at 9:27 PM, Felipe Balbi <balbi@xxxxxx> wrote: On Thu, Mar 28, 2013 at 03:23:46PM +0200, Felipe Balbi wrote: > Hi, > > On Thu, Mar 28, 2013 at 08:53:03PM +0800, Ming Lei wrote: > > On Thu, Mar 28, 2013 at 8:30 PM, B, Ravi <ravibabu@xxxxxx> wrote: > > > > > > For example, in one iteration I have observed, the time taken by > > > uvc_video_decode_isoc() was 2175 usec. In this maximum amount of > > > time was consumed by uvc_video_decode_data() around 1792 usec. > > > > uvc_video_decode_data() is basically a memcpy() from coherent buffer to > > normal buffer. > > if that's the case, this should show, right ? > Maybe not, it might be worse(per my previous test on Pandaboard A1) to > change to DMA streaming buffer, since DMA unmapping has become > expensive too for reading from device after invalidating buffer is added > to handle speculative prefetching, and before that, DMA unmapping was > basically a nop on ARM. > But you guys can do the test again, or do some analysis about such slow > memcpy() on coherent buffer. Since the uvc_video_complete() callback handler called from interrupt context, video post processing or memcpy can be deferred to tasklet or bottom half, rather than doing it in interrupt context. >It is not odd to see I/O performance isn't very good on ARM... -- Ravi B -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
