From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 001C2C64EB1 for ; Fri, 7 Dec 2018 06:24:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9BE3420850 for ; Fri, 7 Dec 2018 06:24:14 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9BE3420850 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=davemloft.net Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726030AbeLGGYN (ORCPT ); Fri, 7 Dec 2018 01:24:13 -0500 Received: from shards.monkeyblade.net ([23.128.96.9]:49778 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725948AbeLGGYN (ORCPT ); Fri, 7 Dec 2018 01:24:13 -0500 Received: from localhost (unknown [IPv6:2601:601:9f80:35cd::bf5]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) (Authenticated sender: davem-davemloft) by shards.monkeyblade.net (Postfix) with ESMTPSA id 269CD147E6BB3; Thu, 6 Dec 2018 22:24:12 -0800 (PST) Date: Thu, 06 Dec 2018 22:24:09 -0800 (PST) Message-Id: <20181206.222409.551374562843523036.davem@davemloft.net> To: pabeni@redhat.com Cc: netdev@vger.kernel.org, eric.dumazet@gmail.com, pjt@google.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH net-next v2 0/4] net: mitigate retpoline overhead From: David Miller In-Reply-To: References: X-Mailer: Mew version 6.8 on Emacs 26.1 Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.5.12 (shards.monkeyblade.net [149.20.54.216]); Thu, 06 Dec 2018 22:24:12 -0800 (PST) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@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!