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Message-ID: <d6348bf0-0da8-c0ae-ce78-7f4620837f66@huawei.com> Date: Wed, 17 May 2023 17:41:31 +0800 From: Yunsheng Lin <linyunsheng@...wei.com> To: Lorenzo Bianconi <lorenzo@...nel.org>, Maciej Fijalkowski <maciej.fijalkowski@...el.com> CC: Lorenzo Bianconi <lorenzo.bianconi@...hat.com>, <netdev@...r.kernel.org>, <bpf@...r.kernel.org>, <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>, <pabeni@...hat.com>, <ast@...nel.org>, <daniel@...earbox.net>, <hawk@...nel.org>, <john.fastabend@...il.com> Subject: Re: [RFC net-next] net: veth: reduce page_pool memory footprint using half page per-buffer On 2023/5/17 6:52, Lorenzo Bianconi wrote: >> On Mon, May 15, 2023 at 01:24:20PM +0200, Lorenzo Bianconi wrote: >>>> On 2023/5/12 21:08, Lorenzo Bianconi wrote: >>>>> In order to reduce page_pool memory footprint, rely on >>>>> page_pool_dev_alloc_frag routine and reduce buffer size >>>>> (VETH_PAGE_POOL_FRAG_SIZE) to PAGE_SIZE / 2 in order to consume one page >>>> >>>> Is there any performance improvement beside the memory saving? As it >>>> should reduce TLB miss, I wonder if the TLB miss reducing can even >>>> out the cost of the extra frag reference count handling for the >>>> frag support? >>> >>> reducing the requested headroom to 192 (from 256) we have a nice improvement in >>> the 1500B frame case while it is mostly the same in the case of paged skb >>> (e.g. MTU 8000B). >> >> Can you define 'nice improvement' ? ;) >> Show us numbers or improvement in %. > > I am testing this RFC patch in the scenario reported below: > > iperf tcp tx --> veth0 --> veth1 (xdp_pass) --> iperf tcp rx > > - 6.4.0-rc1 net-next: > MTU 1500B: ~ 7.07 Gbps > MTU 8000B: ~ 14.7 Gbps > > - 6.4.0-rc1 net-next + page_pool frag support in veth: > MTU 1500B: ~ 8.57 Gbps > MTU 8000B: ~ 14.5 Gbps > Thanks for sharing the data. Maybe using the new frag interface introduced in [1] bring back the performance for the MTU 8000B case. 1. https://patchwork.kernel.org/project/netdevbpf/cover/20230516124801.2465-1-linyunsheng@huawei.com/ I drafted a patch for veth to use the new frag interface, maybe that will show how veth can make use of it. Would you give it a try to see if there is any performance improvment for MTU 8000B case? Thanks. --- a/drivers/net/veth.c +++ b/drivers/net/veth.c @@ -737,8 +737,8 @@ static int veth_convert_skb_to_xdp_buff(struct veth_rq *rq, skb_shinfo(skb)->nr_frags || skb_headroom(skb) < XDP_PACKET_HEADROOM) { u32 size, len, max_head_size, off; + struct page_pool_frag *pp_frag; struct sk_buff *nskb; - struct page *page; int i, head_off; /* We need a private copy of the skb and data buffers since @@ -752,14 +752,20 @@ static int veth_convert_skb_to_xdp_buff(struct veth_rq *rq, if (skb->len > PAGE_SIZE * MAX_SKB_FRAGS + max_head_size) goto drop; + size = min_t(u32, skb->len, max_head_size); + size += VETH_XDP_HEADROOM; + size += SKB_DATA_ALIGN(sizeof(struct skb_shared_info)); + /* Allocate skb head */ - page = page_pool_dev_alloc_pages(rq->page_pool); - if (!page) + pp_frag = page_pool_dev_alloc_frag(rq->page_pool, size); + if (!pp_frag) goto drop; - nskb = napi_build_skb(page_address(page), PAGE_SIZE); + nskb = napi_build_skb(page_address(pp_frag->page) + pp_frag->offset, + pp_frag->truesize); if (!nskb) { - page_pool_put_full_page(rq->page_pool, page, true); + page_pool_put_full_page(rq->page_pool, pp_frag->page, + true); goto drop; } @@ -782,16 +788,18 @@ static int veth_convert_skb_to_xdp_buff(struct veth_rq *rq, len = skb->len - off; for (i = 0; i < MAX_SKB_FRAGS && off < skb->len; i++) { - page = page_pool_dev_alloc_pages(rq->page_pool); - if (!page) { + size = min_t(u32, len, PAGE_SIZE); + + pp_frag = page_pool_dev_alloc_frag(rq->page_pool, size); + if (!pp_frag) { consume_skb(nskb); goto drop; } - size = min_t(u32, len, PAGE_SIZE); - skb_add_rx_frag(nskb, i, page, 0, size, PAGE_SIZE); - if (skb_copy_bits(skb, off, page_address(page), - size)) { + skb_add_rx_frag(nskb, i, pp_frag->page, pp_frag->offset, + size, pp_frag->truesize); + if (skb_copy_bits(skb, off, page_address(pp_frag->page) + + pp_frag->offset, size)) { consume_skb(nskb); goto drop; } @@ -1047,6 +1055,8 @@ static int veth_create_page_pool(struct veth_rq *rq) return err; } + page_pool_set_max_frag_size(rq->page_pool, PAGE_SIZE / 2); + return 0; }
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