On Wed, 22 Feb 2017 18:06:58 -0800 Eric Dumazet <eric.duma...@gmail.com> wrote:
> On Wed, 2017-02-22 at 17:08 -0800, Alexander Duyck wrote: > > > > > Right but you were talking about using both halves one after the > > other. If that occurs you have nothing left that you can reuse. That > > was what I was getting at. If you use up both halves you end up > > having to unmap the page. > > > > You must have misunderstood me. FYI, I also misunderstood you (Eric) to start with ;-) > Once we use both halves of a page, we _keep_ the page, we do not unmap > it. > > We save the page pointer in a ring buffer of pages. > Call it the 'quarantine' > > When we _need_ to replenish the RX desc, we take a look at the oldest > entry in the quarantine ring. > > If page count is 1 (or pagecnt_bias if needed) -> we immediately reuse > this saved page. > > If not, _then_ we unmap and release the page. > > Note that we would have received 4096 frames before looking at the page > count, so there is high chance both halves were consumed. > > To recap on x86 : > > 2048 active pages would be visible by the device, because 4096 RX desc > would contain dma addresses pointing to the 4096 halves. > > And 2048 pages would be in the reserve. I do like it, and it should work. I like it because it solves my concern, regarding being able to adjust the amount of outstanding-frames independently of the RX ring size. Do notice: driver developers have to use Alex'es new DMA API in-order to get writable-pages, else this will violate the DMA API. And XDP requires writable pages. -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer
