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The hyperv NIC driver does memory allocation and copy even without XDP. In XDP mode it will allocate a new page for each packet and copy over the payload, before invoking the XDP BPF-prog. The positive thing it that its easy to determine the xdp.frame_sz. The XDP implementation for hv_netvsc transparently passes xdp_prog to the associated VF NIC. Many of the Azure VMs are using SRIOV, so majority of the data are actually processed directly on the VF driver's XDP path. So the overhead of the synthetic data path (hv_netvsc) is minimal. Then XDP is enabled on this driver, XDP_PASS and XDP_TX will create the SKB via build_skb (based on the newly allocated page). Now using XDP frame_sz this will provide more skb_tailroom, which netstack can use for SKB coalescing (e.g tcp_try_coalesce -> skb_try_coalesce). V3: Adjust patch desc to be more positive. Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Cc: Wei Liu <wei.liu@kernel.org> Cc: "K. Y. Srinivasan" <kys@microsoft.com> Cc: Haiyang Zhang <haiyangz@microsoft.com> Cc: Stephen Hemminger <sthemmin@microsoft.com> Link: https://lore.kernel.org/bpf/158945339857.97035.10212138582505736163.stgit@firesoul
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.