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=-13.2 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,FSL_HELO_FAKE, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_IN_DEF_DKIM_WL 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 2B842C64E8A for ; Wed, 2 Dec 2020 11:20:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CA85222206 for ; Wed, 2 Dec 2020 11:20:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729642AbgLBLTw (ORCPT ); Wed, 2 Dec 2020 06:19:52 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41474 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729639AbgLBLTu (ORCPT ); Wed, 2 Dec 2020 06:19:50 -0500 Received: from mail-wm1-x342.google.com (mail-wm1-x342.google.com [IPv6:2a00:1450:4864:20::342]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 038CEC0613D4 for ; Wed, 2 Dec 2020 03:19:10 -0800 (PST) Received: by mail-wm1-x342.google.com with SMTP id k10so6140512wmi.3 for ; Wed, 02 Dec 2020 03:19:09 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=ewAnY9HSoLrwnuLqpq3pGLIFg/YPcBbyKf1iWj4MkbA=; b=SuUi2UNdeECiQI1YSBC0mxVpJJG47QJ2Uu3Xr3Iwo/yYJnR50iGUodcrQ+mWbq8sDj GuVgRRdNS98KgJnPOT5gOYkOhY8v6I5wzFXVoRtB26wXFskkWi5t9vNlsCfRwdFg/tBk 7FMUbQK3ciWtkewja+gJSHRH54E5+3LQrE8aoXZsgsuy+/QCDfEofXt2rhyE/aHSxYjE hsq3iLDyHExIv9BaOgZA859kcMSjwbkVeJOG3FJTsy7RvHo7g+m1Mm/1jk5mUbkZbTjy eQUhRCTOzRNvF1COg9f22LaIoSRQs/LtVijYenTDZPp/IxQJ8C0+O8CA63OTCOG8zLgn yhwg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=ewAnY9HSoLrwnuLqpq3pGLIFg/YPcBbyKf1iWj4MkbA=; b=afZsKsLCXCbvGOTFE3Po5exyEfZ2N+PTY7C0bsuTukgfyCaIlWI4dnCHXHl8bg8YJn QGfrJpdgVUOtaru3AIriAYoXvFt1QllFG7Rx5UxBlf2s6XBkjGlmhFVi2qUZ6o1KjEwK +PXDdaj8E5KrytxMQlxeWfY0B13Ze0h7YgNnUwK636JRbJuPVBegn3y+NctRwtQVjLnr jO5yxlJa6E4ifS+54UQ6qWWVZHYBl6IUrOhq2Gk0aSnyCSk0EnLwrmSHe1Hv9J1rvUvx uw4UqKQ34ORCs5Wp5DpLeds68ngAwEO5eNUtSEuZ8lX526U7Krqiryu3mG4CCrymDoW0 9LMA== X-Gm-Message-State: AOAM530yZuaxhbYErQ/iycSDdz0TwYWdnGETPe8jVRwfULn4KlBYCVxu KzovgYFm1Hbg+1+o1qv0eaVmVg== X-Google-Smtp-Source: ABdhPJzwJjh1gbEnPTQME3N1fYzMAHiKKDk/w6rK6zdqwhM1akQs6qm0CvuPLF+PBHn0Aju/q3j3sg== X-Received: by 2002:a7b:cf08:: with SMTP id l8mr2615389wmg.189.1606907947170; Wed, 02 Dec 2020 03:19:07 -0800 (PST) Received: from google.com (203.75.199.104.bc.googleusercontent.com. [104.199.75.203]) by smtp.gmail.com with ESMTPSA id 34sm1578880wrh.78.2020.12.02.03.19.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 02 Dec 2020 03:19:06 -0800 (PST) Date: Wed, 2 Dec 2020 11:19:02 +0000 From: Brendan Jackman To: Alexei Starovoitov Cc: Yonghong Song , bpf , Alexei Starovoitov , Daniel Borkmann , KP Singh , Florent Revest , LKML , Jann Horn Subject: Re: [PATCH v2 bpf-next 10/13] bpf: Add instructions for atomic[64]_[fetch_]sub Message-ID: <20201202111902.GC9710@google.com> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Tue, Dec 01, 2020 at 09:55:22PM -0800, Alexei Starovoitov wrote: > 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. Ack, I'll drop the atomic subtract instruction.