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    Subject[PATCH net-next v2 0/4] net: mitigate retpoline overhead
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    The spectre v2 counter-measures, aka retpolines, are a source of measurable
    overhead[1]. We can partially address that when the function pointer refers to
    a builtin symbol resorting to a list of tests vs well-known builtin function and
    direct calls.

    Experimental results show that replacing a single indirect call via
    retpoline with several branches and a direct call gives performance gains
    even when multiple branches are added - 5 or more, as reported in [2].

    This may lead to some uglification around the indirect calls. In netconf 2018
    Eric Dumazet described a technique to hide the most relevant part of the needed
    boilerplate with some macro help.

    This series is a [re-]implementation of such idea, exposing the introduced
    helpers in a new header file. They are later leveraged to avoid the indirect
    call overhead in the GRO path, when possible.

    Overall this gives > 10% performance improvement for UDP GRO benchmark and
    smaller but measurable for TCP syn flood.

    The added infra can be used in follow-up patches to cope with retpoline overhead
    in other points of the networking stack (e.g. at the qdisc layer) and possibly
    even in other subsystems.

    rfc -> v1:
    - use branch prediction hints, as suggested by Eric

    v1 -> v2:
    - list explicitly the builtin function names in INDIRECT_CALL_*()
    - expand the recipients list

    [1] http://vger.kernel.org/netconf2018_files/PaoloAbeni_netconf2018.pdf
    [2] https://linuxplumbersconf.org/event/2/contributions/99/attachments/98/117/lpc18_paper_af_xdp_perf-v2.pdf

    Paolo Abeni (4):
    indirect call wrappers: helpers to speed-up indirect calls of builtin
    net: use indirect call wrappers at GRO network layer
    net: use indirect call wrappers at GRO transport layer
    udp: use indirect call wrappers for GRO socket lookup

    include/linux/indirect_call_wrapper.h | 51 +++++++++++++++++++++++++++
    include/net/inet_common.h | 9 +++++
    net/core/dev.c | 15 ++++++--
    net/ipv4/af_inet.c | 13 +++++--
    net/ipv4/tcp_offload.c | 6 ++--
    net/ipv4/udp_offload.c | 15 +++++---
    net/ipv6/ip6_offload.c | 18 +++++++---
    net/ipv6/tcpv6_offload.c | 7 ++--
    net/ipv6/udp_offload.c | 7 ++--
    9 files changed, 119 insertions(+), 22 deletions(-)
    create mode 100644 include/linux/indirect_call_wrapper.h

    --
    2.19.2

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