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=-2.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 69871C64E8A for ; Wed, 2 Dec 2020 05:56:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 12BE8221FE for ; Wed, 2 Dec 2020 05:56:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725984AbgLBF4P (ORCPT ); Wed, 2 Dec 2020 00:56:15 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48070 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725979AbgLBF4P (ORCPT ); Wed, 2 Dec 2020 00:56:15 -0500 Received: from mail-lj1-x244.google.com (mail-lj1-x244.google.com [IPv6:2a00:1450:4864:20::244]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id ED278C0613CF; Tue, 1 Dec 2020 21:55:34 -0800 (PST) Received: by mail-lj1-x244.google.com with SMTP id o24so1325474ljj.6; Tue, 01 Dec 2020 21:55:34 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=kF4MPMV0LOJFs58rVTILZsCl7WhPqj7BoWapl4MSIas=; b=LIKmg7gOf5TQqHOFN6bHxs0M12fOa+pXJ7zQlWfL1sTD+bnafY7ILuk7noKX8yem7/ rcBma/TUWGFd38s0xp5T6sq+WmqxI/P3niWjVmTWKF49OfkRt7194nK/OzvKzRr/Ytzv bVV9OY86nwVPyvmU755Sj0i/yrGjerUGNAYCa0U/o8PW/HQLIe3Ihq+UsVw6myrstixc rzm2LkDj3hY36Io9HMyIjCvK7ElEap6qtqDuoJ7AjiL8X8DMkpPxUaPZatOySfWAnyjh 0CxCkTnCtdjFBaXYcQNZ8SjGNmkfc7cYZi+UoqW6cAiGNPLqgjzRLBdCUYUlEj0Hs5bt 9Erw== 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=kF4MPMV0LOJFs58rVTILZsCl7WhPqj7BoWapl4MSIas=; b=PV8SCHKH1KGP+AM7a7x9fgC15sn7o7Jys0Zip690qnYJgcmon++3+SX2yy9wP8PbhN xDOR/jbEp1Sog0m1cIgwBNQZ7jZvl0gPkmTg2swWheG3vMzshh9reH+5ARfOi8fd4vF7 1lsGJ9ZSFZTNMOfbK9W0PY5NskFF5VlLNoMnUlCxbknvkKAlRwWV7974h3PAJWGLDaG8 9Vwi8rShk6mAxepQ7egHp5++32t10FQDHY0KXH/JGMgzcclKmT+PPNKtwUtusSHMtdOn 0s3IXFTZuPTy80+yi5efE6AiLoFKaCl1iF2JxT/kvh0TH20i8z8QGZEs6m8kS8CH64Kc mH7w== X-Gm-Message-State: AOAM533oKsfonBlmwhzdW2HuO33m2OIRj0bVmtJYMzDWI0l9Q9hyNbHc wSwC1XDf2iqFf2tC1L+va1qyhdU3GmPHHCwv2UI= X-Google-Smtp-Source: ABdhPJxpsSmdSgqny8SdbIFxHHYUYtZQ7tUeZribhUihDQV3zusMP9ezIy4Vv+1oLdorBk82qON8qsOQ/HV18yF6U74= X-Received: by 2002:a2e:8982:: with SMTP id c2mr455784lji.121.1606888533502; Tue, 01 Dec 2020 21:55:33 -0800 (PST) MIME-Version: 1.0 References: <20201127175738.1085417-1-jackmanb@google.com> <20201127175738.1085417-11-jackmanb@google.com> <0fd52966-24b2-c50c-4f23-93428d8993c4@fb.com> <20201129013420.yi7ehnseawm5hsb7@ast-mbp> <1dfd2e5e-f8d2-eac2-d6b2-7428ceb00c36@fb.com> <20201201123800.GG2114905@google.com> In-Reply-To: <20201201123800.GG2114905@google.com> From: Alexei Starovoitov Date: Tue, 1 Dec 2020 21:55:22 -0800 Message-ID: Subject: Re: [PATCH v2 bpf-next 10/13] bpf: Add instructions for atomic[64]_[fetch_]sub To: Brendan Jackman Cc: Yonghong Song , bpf , Alexei Starovoitov , Daniel Borkmann , KP Singh , Florent Revest , LKML , Jann Horn Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Tue, Dec 1, 2020 at 4:38 AM Brendan Jackman wrote: > > I guess it's also worth remembering other archs might have an atomic > subtract. which one? arm64 LSE implements atomic_fetch_sub as neg+ldadd. imo x64 and arm64 example outweighs choices by other archs if there are such. Even without LSE it will be neg+llsc loop. The reason I proposed bpf xsub insn earlier is that I thought that llvm won't be able to emit it so easily and JIT/verifier would struggle.