From: Paolo Abeni <pab...@redhat.com> Date: Wed, 5 Dec 2018 19:13:38 +0100
> 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. ... Series applied, thanks!
