Re: [PATCH net] virtio-net: drop the multi-buffer XDP packet in zerocopy
From: Jakub Kicinski <kuba@kernel.org>
Date: 2025-06-10 20:37:52
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bpf, lkml, stable, virtualization
On Tue, 10 Jun 2025 22:18:32 +0700 Bui Quang Minh wrote:
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Furthermore, we are in the zerocopy so we cannot linearize by allocating a large enough buffer to cover the whole frame then copy the frame data to it. That's not zerocopy anymore. Also, XDP socket zerocopy receive has assumption that the packet it receives must from the umem pool. AFAIK, the generic XDP path is for copy mode only.Generic XDP == do_xdp_generic(), here I think you mean the normal XDP patch in the virtio driver? If so then no, XDP is very much not expected to copy each frame before processing.Yes, I mean generic XDP = do_xdp_generic(). I mean that we can linearize the frame if needed (like in netif_skb_check_for_xdp()) in copy mode for XDP socket but not in zerocopy mode.
Okay, I meant the copies in the driver - virtio calls xdp_linearize_page() in a few places, for normal XDP.
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This is only slightly related to you patch but while we talk about multi-buf - in the netdev CI the test which sends ping while XDP multi-buf program is attached is really flaky :( https://netdev.bots.linux.dev/contest.html?executor=vmksft-drv-hw&test=ping-py.ping-test-xdp-native-mb&ld-cases=1metal-drv-hw means the NETIF is the real NIC, right?
The "metal" in the name refers to the AWS instance type that hosts the runner. The test runs in a VM over virtio, more details: https://github.com/linux-netdev/nipa/wiki/Running-driver-tests-on-virtio