From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH net-next v2 0/4] net: mitigate retpoline overhead Date: Thu, 06 Dec 2018 22:24:09 -0800 (PST) Message-ID: <20181206.222409.551374562843523036.davem@davemloft.net> References: Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, eric.dumazet@gmail.com, pjt@google.com, linux-kernel@vger.kernel.org To: pabeni@redhat.com Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org From: Paolo Abeni 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!