In data mercoledì 1 agosto 2012 07:04:18, Jonathan Corbet ha scritto: > On Wed, 1 Aug 2012 08:41:56 +0200 > > Hans Verkuil <hverkuil@xxxxxxxxx> wrote: > > > The second patch adds a new memory allocator for the videobuf2. I > > > name it videobuf2-dma-streaming but I think "streaming" is not > > > the best choice, so suggestions are welcome. My inspiration for > > > this buffer come from videobuf-dma-contig (cached) version. After > > > I made this buffer I found the videobuf2-dma-nc made by Jonathan > > > Corbet and I improve the allocator with some suggestions > > > (http://patchwork.linuxtv.org/patch/7441/). The VIP doesn't work > > > with videobu2-dma-contig and I think this solution is easier the > > > sg.> > > I leave this to the vb2 experts. It's not obvious to me why we would > > need a fourth memory allocator. > > I first wrote my version after observing that performance dropped by a > factor of three on the OLPC XO 1.75 when using contiguous, coherent > memory. If the architecture needs to turn off caching, things really > slow down, to the point that it's unusable. There's no real reason > why a V4L2 device shouldn't be able to use streaming mappings in this > situation; it performs better and doesn't eat into the limited > amounts of coherent DMA space available on some systems. > > I never got my version into a mergeable state only because I finally > figured out how to bludgeon the hardware into doing s/g DMA and didn't > need it anymore. But I think it's a worthwhile functionality to > have, and, with CMA, it could be the preferred mode for a number of > devices. > > jon I think that the memory allocator is the most questionable patch, but if there are not any other comments I will send my three patches for the inclusion. It is summer, time for vacation, so I'll wait for another week or two for critical comments and then I will send patches. -- Federico Vaga -- 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
