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Message-ID: <a7e72202-0fa1-633e-1564-132a1984aba1@redhat.com> Date: Mon, 21 Aug 2023 23:54:34 +0200 From: Jesper Dangaard Brouer <jbrouer@...hat.com> To: Liang Chen <liangchen.linux@...il.com>, hawk@...nel.org, horms@...nel.org, davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, linyunsheng@...wei.com Cc: brouer@...hat.com, ilias.apalodimas@...aro.org, daniel@...earbox.net, ast@...nel.org, netdev@...r.kernel.org, Lorenzo Bianconi <lorenzo.bianconi@...hat.com>, Stanislav Fomichev <sdf@...gle.com>, Maryam Tahhan <mtahhan@...hat.com> Subject: Re: [RFC PATCH net-next v3 0/2] net: veth: Optimizing page pool usage On 21/08/2023 16.21, Jesper Dangaard Brouer wrote: > > On 16/08/2023 14.30, Liang Chen wrote: >> Page pool is supported for veth, but at the moment pages are not properly >> recyled for XDP_TX and XDP_REDIRECT. That prevents veth xdp from fully >> leveraging the advantages of the page pool. So this RFC patchset is >> mainly >> to make recycling work for those cases. With that in place, it can be >> further optimized by utilizing the napi skb cache. Detailed figures are >> presented in each commit message, and together they demonstrate a quite >> noticeable improvement. >> > > I'm digging into this code path today. > > I'm trying to extend this and find a way to support SKBs that used > kmalloc (skb->head_frag=0), such that we can remove the > skb_head_is_locked() check in veth_convert_skb_to_xdp_buff(), which will > allow more SKBs to avoid realloc. As long as they have enough headroom, > which we can dynamically control for netdev TX-packets by adjusting > netdev->needed_headroom, e.g. when loading an XDP prog. > > I noticed netif_receive_generic_xdp() and bpf_prog_run_generic_xdp() can > handle SKB kmalloc (skb->head_frag=0). Going though the code, I don't > think it is a bug that generic-XDP allows this. > > Deep into this rabbit hole, I start to question our approach. > - Perhaps the veth XDP approach for SKBs is wrong? > > The root-cause of this issue is that veth_xdp_rcv_skb() code path (that > handle SKBs) is calling XDP-native function "xdp_do_redirect()". I > question, why isn't it using "xdp_do_generic_redirect()"? > (I will jump into this rabbit hole now...) It works, implemented using xdp_do_generic_redirect() and lifted skb_head_is_locked check in veth_convert_skb_to_xdp_buff(), plus adjust xsk_build_skb() to alloc enough headroom. The results[1] are good approx 26% faster[1] compared to Maryam's veth-benchmark[3] results[2]. --Jesper [1] https://github.com/xdp-project/xdp-project/blob/veth-benchmark02/areas/core/veth_benchmark04.org#implemented-use-generic-xdp-redirect [2] https://github.com/xdp-project/xdp-project/blob/veth-benchmark02/areas/core/veth_benchmark03.org#benchmark01-with-xdp-redirect-loaded-on-host-veth [3] https://github.com/maryamtahhan/veth-benchmark/
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