Le mardi 31 juillet 2012 17:03:52 Rob Clark, vous avez écrit : > On Tue, Jul 31, 2012 at 8:39 AM, Rémi Denis-Courmont <remi@xxxxxxxxxx> wrote: > > Le mardi 31 juillet 2012 14:56:14 Laurent Pinchart, vous avez écrit : > >> > For that matter, wouldn't it be useful to support exporting a userptr > >> > buffer at some point in the future? > >> > >> Shouldn't USERPTR usage be discouraged once we get dma-buf support ? > > > > USERPTR, where available, is currently the only way to perform zero-copy > > from kernel to userspace. READWRITE does not support zero-copy at all. > > MMAP only supports zero-copy if userspace knows a boundary on the number > > of concurrent buffers *and* the device can deal with that number of > > buffers; in general, MMAP requires memory copying. > > hmm, this sounds like the problem is device pre-allocating buffers? Basically, yes. > Anyways, last time I looked, the vb2 core supported changing dmabuf fd > each time you QBUF, in a similar way to what you can do w/ userptr. > So that seems to get you the advantages you miss w/ mmap without the > pitfalls of userptr. It might work albeit with a higher system calls count overhead. But what about libv4l2 transparent format conversion? Emulated USERBUF, with MMAP in the back-end would provide by far the least overhead. I don't see how DMABUF would work there. -- Rémi Denis-Courmont http://www.remlab.net/ http://fi.linkedin.com/in/remidenis -- 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
