On Thu, 10 Oct 2019 01:18:34 +0200 Lorenzo Bianconi <lore...@kernel.org> wrote:
> mvneta driver can run on not cache coherent devices so it is > necessary to sync dma buffers before sending them to the device > in order to avoid memory corruption. This patch introduce a performance > penalty and it is necessary to introduce a more sophisticated logic > in order to avoid dma sync as much as we can Report with benchmarks here: https://github.com/xdp-project/xdp-project/blob/master/areas/arm64/board_espressobin08_bench_xdp.org We are testing this on an Espressobin board, and do see a huge performance cost associated with this DMA-sync. Regardless we still want to get this patch merged, to move forward with XDP support for this driver. We promised each-other (on IRC freenode #xdp) that we will follow-up with a solution/mitigation, after this patchset is merged. There are several ideas, that likely should get separate upstream review. > Signed-off-by: Lorenzo Bianconi <lore...@kernel.org> Signed-off-by: Jesper Dangaard Brouer <bro...@redhat.com> > --- > drivers/net/ethernet/marvell/mvneta.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/drivers/net/ethernet/marvell/mvneta.c > b/drivers/net/ethernet/marvell/mvneta.c > index 79a6bac0192b..ba4aa9bbc798 100644 > --- a/drivers/net/ethernet/marvell/mvneta.c > +++ b/drivers/net/ethernet/marvell/mvneta.c > @@ -1821,6 +1821,7 @@ static int mvneta_rx_refill(struct mvneta_port *pp, > struct mvneta_rx_queue *rxq, > gfp_t gfp_mask) > { > + enum dma_data_direction dma_dir; > dma_addr_t phys_addr; > struct page *page; > > @@ -1830,6 +1831,9 @@ static int mvneta_rx_refill(struct mvneta_port *pp, > return -ENOMEM; > > phys_addr = page_pool_get_dma_addr(page) + pp->rx_offset_correction; > + dma_dir = page_pool_get_dma_dir(rxq->page_pool); > + dma_sync_single_for_device(pp->dev->dev.parent, phys_addr, > + MVNETA_MAX_RX_BUF_SIZE, dma_dir); > mvneta_rx_desc_fill(rx_desc, phys_addr, page, rxq); > > return 0; -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer
