From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) by sourceware.org (Postfix) with ESMTP id 6FF9F3855026 for ; Sat, 17 Jul 2021 21:37:48 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 6FF9F3855026 Received: from mail-pg1-f199.google.com (mail-pg1-f199.google.com [209.85.215.199]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-337-BJqsAqzANp-bKyzWS2ISiA-1; Sat, 17 Jul 2021 17:37:46 -0400 X-MC-Unique: BJqsAqzANp-bKyzWS2ISiA-1 Received: by mail-pg1-f199.google.com with SMTP id z30-20020a630a5e0000b029022c78a7fc98so10504286pgk.11 for ; Sat, 17 Jul 2021 14:37:46 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=wd38EQfX0ZLE1vA7gxO8koS/UoFHdMNIkBEgFfBYu3w=; b=VKyaImK0KCQtE3h4WfHqZV+s76kJkIPkGXNNv5y44O/SAhN2JM7GYur9mLmoTeD1qs XGbfDJGATd7TzNWwPG07Z/VsrqDztFqqYO5MvWSqZQcgXBk8fHAH+7JgQWvsmOoRi8kE jbVxrktJoWEYtEyO0mlE4vXc5LKcx0644hP82/g++xmTD7BoKpKJvkE0wvTkN1ywYp5O dzClvc+TwAIQcvoCoXrks76zNxyvkZ5GydygopRrVqrVN5A27dbAiWZCris+fqgTSZD4 nEMtJwj8U/aEQYyFgDQR1cs8Rusl1UGGRyqbwhYU2/XsEQXmWlbIiNSZcamU4thOMdLA CVPw== X-Gm-Message-State: AOAM530oGRIDR0hDqzvERzNekBmVjKjxdFTc2HWOSmhZOA08hGifdYF+ +F9zwpyL8GbaEuz94EiL6P0J5Mdq9U+sbNESnRWKigcDrIH2utuPawctpCtt2wj/YIIzGeud6FW IYUd0rSrvq08gXdOZkWPas9+mD+cXn4w2nEr4 X-Received: by 2002:aa7:8d56:0:b029:327:6dc:d254 with SMTP id s22-20020aa78d560000b029032706dcd254mr17399069pfe.69.1626557865294; Sat, 17 Jul 2021 14:37:45 -0700 (PDT) X-Google-Smtp-Source: ABdhPJy7Wdnufa5u1yDjSVb0novSJckIlxmka+NS8ZsUHu0jXmpM+9ORJ7goSCS+FqlLzqK7iaRShIL9Na9hrThVMF8= X-Received: by 2002:aa7:8d56:0:b029:327:6dc:d254 with SMTP id s22-20020aa78d560000b029032706dcd254mr17399050pfe.69.1626557864971; Sat, 17 Jul 2021 14:37:44 -0700 (PDT) MIME-Version: 1.0 References: <20210716023656.670004-1-jason@redhat.com> <3179041.TO5rdG3zkT@excalibur> <90365047.B8guWdUDZo@excalibur> In-Reply-To: <90365047.B8guWdUDZo@excalibur> From: Jason Merrill Date: Sat, 17 Jul 2021 14:37:33 -0700 Message-ID: Subject: Re: [PATCH] c++: implement C++17 hardware interference size To: Matthias Kretz Cc: Jonathan Wakely , Jonathan Wakely , "Richard Earnshaw (lists)" , "libstdc++" , gcc-patches List , GNU C Library X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com X-Spam-Status: No, score=-6.5 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, HTML_MESSAGE, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H4, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_NONE, TXREP autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Content-Filtered-By: Mailman/MimeDel 2.1.29 X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 17 Jul 2021 21:37:50 -0000 On Sat, Jul 17, 2021 at 6:55 AM Matthias Kretz wrote: > On Saturday, 17 July 2021 15:32:42 CEST Jonathan Wakely wrote: > > On Sat, 17 Jul 2021, 09:15 Matthias Kretz, wrote: > > > If somebody writes a library with `keep_apart` in the public API/ABI > then > > > you're right. > > > > Yes, it's fine if those constants don't affect anything across module > > boundaries. > > I believe a significant fraction of hardware interference size usage will > be > internal. > I would hope for this to be the vast majority of usage. I want the warning to discourage people from using the interference size variables in the public API of a library. > > > The developer who wants his code to be included in a distro should ca= re > > > about > > > binary distribution. If his code has an ABI issue, that's a bug he > needs > > > to > > > fix. It's not the fault of the packager. > > > > Yes but in practice it's the packagers who have to deal with the bug > > reports, analyze the problem, and often fix the bug too. It might not b= e > > the packager's fault but it's often their problem > > I can imagine. But I don't think requiring users to specify the value > according to what -mtune suggests will improve things. Users will write a > configure/cmake/... macro to parse the value -mtune prints and pass that > on > the command line (we'll soon find this solution on SO =F0=9F=98=9C). I.e.= things are > likely to be even more broken. Simpler would be a flag to say "set them based on -mtune", e.g. -finterference-tuning or --param destructive-intereference-size=3Dtuning. That would be just as easy to write as -Wno-interference-size. Jason