HI Jesper, Ivan, > On Wed, 3 Jul 2019 12:37:50 +0200 > Jose Abreu <jose.ab...@synopsys.com> wrote: > > > @@ -3547,6 +3456,9 @@ static int stmmac_rx(struct stmmac_priv *priv, int > > limit, u32 queue) > > > > napi_gro_receive(&ch->rx_napi, skb); > > > > + page_pool_recycle_direct(rx_q->page_pool, buf->page); > > This doesn't look correct. > > 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). > > You will have to call: > page_pool_release_page(rx_q->page_pool, buf->page); > > This will do a DMA-unmap, and you will likely loose your performance > gain :-( > > > > + buf->page = NULL; > > + > > priv->dev->stats.rx_packets++; > > priv->dev->stats.rx_bytes += frame_len; > > } > > 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). On our case (and in the page_pool API in general) you have to track buffers when both .ndo_xdp_xmit() and XDP_TX are used. So the lifetime of a packet might be
1. page pool allocs packet. The API doesn't sync but i *think* you don't have to explicitly since the CPU won't touch that buffer until the NAPI handler kicks in. On the napi handler you need to dma_sync_single_for_cpu() and process the packet. 2a) no XDP is required so the packet is unmapped and free'd 2b) .ndo_xdp_xmit is called so tyhe buffer need to be mapped/unmapped 2c) XDP_TX is called. In that case we re-use an Rx buffer so we need to dma_sync_single_for_device() 2a and 2b won't cause any issues In 2c the buffer will be recycled and fed back to the device with a *correct* sync (for_device) and all those buffers are allocated as DMA_BIDIRECTIONAL. So bvottom line i *think* we can skip the dma_sync_single_for_device() on the initial allocation *only*. If am terribly wrong please let me know :) Thanks /Ilias > > > [1] > https://github.com/xdp-project/xdp-project/blob/master/areas/mem/page_pool02_SKB_return_callback.org > -- > Best regards, > Jesper Dangaard Brouer > MSc.CS, Principal Kernel Engineer at Red Hat > LinkedIn: http://www.linkedin.com/in/brouer
