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Paolo Abeni says: ==================== net: mitigate retpoline overhead 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. v2 -> v3: - fix build error with CONFIG_IPV6=m v1 -> v2: - list explicitly the builtin function names in INDIRECT_CALL_*(), as suggested by Ed Cree - expand the recipients list rfc -> v1: - use branch prediction hints, as suggested by Eric [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 ==================== Signed-off-by: David S. Miller <davem@davemloft.net>
Linux kernel
============
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