On Thu, Jul 04, 2019 at 10:13:37AM +0000, Jose Abreu wrote: > From: Jesper Dangaard Brouer <bro...@redhat.com> > > > The page_pool DMA mapping cannot be "kept" when page traveling into the > > network stack attached to an SKB. (Ilias and I have a long term plan[1] > > to allow this, but you cannot do it ATM). > > The reason I recycle the page is this previous call to: > > skb_copy_to_linear_data() > > So, technically, I'm syncing to CPU the page(s) and then memcpy to a > previously allocated SKB ... So it's safe to just recycle the mapping I > think. > > Its kind of using bounce buffers and I do see performance gain in this > (I think the reason is because my setup uses swiotlb for DMA mapping).
Maybe. Have you tested this on big/small packets? Can you do a test with 64b/128b and 1024b for example? The memcpy might be cheap for the small sized packets (and cheaper than the dma map/unmap) > > Anyway, I'm open to some suggestions on how to improve this ... > > > Also remember that the page_pool requires you driver to do the DMA-sync > > operation. I see a dma_sync_single_for_cpu(), but I didn't see a > > dma_sync_single_for_device() (well, I noticed one getting removed). > > (For some HW Ilias tells me that the dma_sync_single_for_device can be > > elided, so maybe this can still be correct for you). > > My HW just needs descriptors refilled which are in different coherent > region so I don't see any reason for dma_sync_single_for_device() ... I am abit overloaded at the moment. I'll try to have a look at this and get back to you Cheers /Ilias
