Hi Mauro, On Friday 18 February 2011 13:33:12 Mauro Carvalho Chehab wrote: > Em 18-02-2011 08:31, Laurent Pinchart escreveu: > > It's a trade-off between memory and speed. Preallocating still image > > capture buffers will give you better snapshot performances, at the > > expense of memory. > > > > The basic problems we have here is that taking snapshots is slow with the > > current API if we need to stop capture, free buffers, change the format, > > allocate new buffers (and perform cache management operations) and > > restart the stream. To fix this we're considering a way to preallocate > > still image capture buffers, but I'm open to proposals for other ways to > > solve the issue :-) > > From the above operations, considering that CMA is used to reserve a > non-shared memory with enough space for the new buffer size/qtd, I don't > think that the most expensive operation would be to realloc the memory. > > The logic to stop/start streaming seems to be the most consuming one, as > driver will need to wait for the current I/O operation to complete, and > this can take hundreds of milisseconds (the duration of one frame). > > How much time would CMA need to free and re-allocate the buffers for, let's > say, something in the range of 1-10 MB, on a pre-allocated, non shared > memory space? CMA won't solve the problem, as not all drivers require continuous memory. The OMAP3 ISP has an IOMMU, and two very time-consuming tasks are mapping the memory to the IOMMU and cleaning the cache. This is why preallocation *and* prequeuing is needed. -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
