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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 21ECDC4320A for ; Sat, 24 Jul 2021 18:51:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 053E360E96 for ; Sat, 24 Jul 2021 18:51:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230093AbhGXSLX (ORCPT ); Sat, 24 Jul 2021 14:11:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44872 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229865AbhGXSLX (ORCPT ); Sat, 24 Jul 2021 14:11:23 -0400 Received: from Chamillionaire.breakpoint.cc (Chamillionaire.breakpoint.cc [IPv6:2a0a:51c0:0:12e:520::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B019FC061575; Sat, 24 Jul 2021 11:51:54 -0700 (PDT) Received: from fw by Chamillionaire.breakpoint.cc with local (Exim 4.92) (envelope-from ) id 1m7MkP-0007qR-Tl; Sat, 24 Jul 2021 20:51:41 +0200 Date: Sat, 24 Jul 2021 20:51:41 +0200 From: Florian Westphal To: Paul Moore Cc: Paolo Abeni , Casey Schaufler , netdev@vger.kernel.org, "David S. Miller" , Jakub Kicinski , Florian Westphal , Eric Dumazet , linux-security-module@vger.kernel.org, selinux@vger.kernel.org Subject: Re: [PATCH RFC 0/9] sk_buff: optimize layout for GRO Message-ID: <20210724185141.GJ9904@breakpoint.cc> References: <1252ad17-3460-5e6a-8f0d-05d91a1a7b96@schaufler-ca.com> <2e9e57f0-98f9-b64d-fd82-aecef84835c5@schaufler-ca.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: Paul Moore wrote: > Tow main drivers on my side: > > - there are use cases/deployments that do not use them. > > - moving them around was doable in term of required changes. > > > > There are no "slow-path" implications on my side. For example, vlan_* > > fields are very critical performance wise, if the traffic is tagged. > > But surely there are busy servers not using tagget traffic which will > > enjoy the reduced cachelines footprint, and this changeset will not > > impact negatively the first case. > > > > WRT to the vlan example, secmark and nfct require an extra conditional > > to fetch the data. My understanding is that such additional conditional > > is not measurable performance-wise when benchmarking the security > > modules (or conntrack) because they have to do much more intersting > > things after fetching a few bytes from an already hot cacheline. > > > > Not sure if the above somehow clarify my statements. > > > > As for expanding secmark to 64 bits, I guess that could be an > > interesting follow-up discussion :) > > The intersection between netdev and the LSM has a long and somewhat > tortured past with each party making sacrifices along the way to get > where we are at today. It is far from perfect, at least from a LSM > perspective, but it is what we've got and since performance is usually > used as a club to beat back any changes proposed by the LSM side, I > would like to object to these changes that negatively impact the LSM > performance without some concession in return. It has been a while > since Casey and I have spoken about this, but I think the prefered > option would be to exchange the current __u32 "sk_buff.secmark" field > with a void* "sk_buff.security" field, like so many other kernel level > objects. Previous objections have eventually boiled down to the > additional space in the sk_buff for the extra bits (there is some > additional editorializing that could be done here, but I'll refrain), > but based on the comments thus far in this thread it sounds like > perhaps we can now make a deal here: move the LSM field down to a > "colder" cacheline in exchange for converting the LSM field to a > proper pointer. > > Thoughts? Is there a summary disucssion somewhere wrt. what exactly LSMs need? There is the skb extension infra, does that work for you?