On 2023/4/23 22:20, Lorenzo Bianconi wrote: >> On 2023/4/23 2:54, Lorenzo Bianconi wrote: >>> struct veth_priv { >>> @@ -727,17 +729,20 @@ static int veth_convert_skb_to_xdp_buff(struct veth_rq *rq, >>> goto drop; >>> >>> /* Allocate skb head */ >>> - page = alloc_page(GFP_ATOMIC | __GFP_NOWARN); >>> + page = page_pool_dev_alloc_pages(rq->page_pool); >>> if (!page) >>> goto drop; >>> >>> nskb = build_skb(page_address(page), PAGE_SIZE); >> >> If page pool is used with PP_FLAG_PAGE_FRAG, maybe there is some additional >> improvement for the MTU 1500B case, it seem a 4K page is able to hold two skb. >> And we can reduce the memory usage too, which is a significant saving if page >> size is 64K. > > please correct if I am wrong but I think the 1500B MTU case does not fit in the > half-page buffer size since we need to take into account VETH_XDP_HEADROOM. > In particular: > > - VETH_BUF_SIZE = 2048 > - VETH_XDP_HEADROOM = 256 + 2 = 258 On some arch the NET_IP_ALIGN is zero. I suppose XDP_PACKET_HEADROOM are for xdp_frame and data_meta, it seems xdp_frame is only 40 bytes for 64 bit arch and max size of metalen is 32 as xdp_metalen_invalid() suggest, is there any other reason why we need 256 bytes here? > - max_headsize = SKB_WITH_OVERHEAD(VETH_BUF_SIZE - VETH_XDP_HEADROOM) = 1470 > > Even in this case we will need the consume a full page. In fact, performances > are a little bit worse: > > MTU 1500: tcp throughput ~ 8.3Gbps > > Do you agree or am I missing something? > > Regards, > Lorenzo