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 Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 83C87C433F5 for ; Tue, 24 May 2022 12:22:29 +0000 (UTC) Received: from localhost ([::1]:50798 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ntTYS-0004O9-D3 for qemu-devel@archiver.kernel.org; Tue, 24 May 2022 08:22:28 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:42284) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ntT1J-0005Lw-Vq for qemu-devel@nongnu.org; Tue, 24 May 2022 07:48:15 -0400 Received: from mail-pf1-x434.google.com ([2607:f8b0:4864:20::434]:42623) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1ntT1I-0003dm-6l for qemu-devel@nongnu.org; Tue, 24 May 2022 07:48:13 -0400 Received: by mail-pf1-x434.google.com with SMTP id y199so16205612pfb.9 for ; Tue, 24 May 2022 04:48:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=message-id:date:mime-version:user-agent:subject:content-language:to :cc:references:from:in-reply-to:content-transfer-encoding; bh=FE0iwfme+sc8UyoN2QM/vJXxcsXcktKneiQYiZkRx1Q=; b=usTiZwbTWaD6jJoFsQguQhXBJRitT96xZb+KKsxILzzsqucUCTe8TbfYoKCrmyzVqK +G1MP2LbBI5qDSDQYPRWTD7CXSySjlPGH/fV5Akont3E8ORjUZw4/75muL7t+Ex9KQym NTpAfDt+3Z/Dy3/XausWjKw3wQO0xMcxkDGx/BUPPFbHOyb6FPLbeIdrYpqBuoWl+oOj zbPsa9xCs8Lv2A3qPesAcKGj1SPHTVmbYdhwRGf9YwT4Td+EOjrvuTT1m2TfrbmAMGek FazLDtVcH987etQ0Isctrsb2N7iL4KzafKplXoD2FvdUl/YC4VO0Zu+d3qFgp19m6pXq pepw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:message-id:date:mime-version:user-agent:subject :content-language:to:cc:references:from:in-reply-to :content-transfer-encoding; bh=FE0iwfme+sc8UyoN2QM/vJXxcsXcktKneiQYiZkRx1Q=; b=lok03d3yHllcJDcWmm1ZBwdXPAPVOO5PwhLr3v5QvcPu9T0Ft1SR/svDB1wpSgpNZM 4UUBNVv947oJahlqbtEkTEZ2rAy98QMeSdZisMAsXwJFpuOCXF4FFieYM8p4J9sM+sJn vcnzWQMChDQZZkz/2t8TMWHfWqdUOPg36yFMjeLAXyBYzvtULS6TQbXnVvSgXFnj/lO1 7VQ1P0IKigJwRVedHYuSx8DoTd8eYvAqYGjuuJGsDx+rlYXopiVBtlj8JzXknQwnkLEi 2hiCmQzxrkgh59GRuf21cZYcm9/eGVEodSJ/UV7SwiF6K5ySjORvXcDURIEYISXAQhsA nvFg== X-Gm-Message-State: AOAM533jP8MPUNPjvfrzcF+LWFIybkS8HThaNjf3XDEcs6n73hi3Fgau UAak3v+nBTtJlAuscHeLXErEoHurmSJS+w== X-Google-Smtp-Source: ABdhPJxK5OHC4T1sTVUVJlF5R1pjuaoXjGjdrFpCvEFTmx/SE6KOrcNtU+EPeK8I2UwmFRY9Z++hbA== X-Received: by 2002:aa7:8492:0:b0:518:7e1a:3359 with SMTP id u18-20020aa78492000000b005187e1a3359mr17281314pfn.18.1653392890920; Tue, 24 May 2022 04:48:10 -0700 (PDT) Received: from [192.168.1.6] ([71.212.142.129]) by smtp.gmail.com with ESMTPSA id h6-20020a170902f70600b0015eb200cc00sm7008519plo.138.2022.05.24.04.48.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 24 May 2022 04:48:10 -0700 (PDT) Message-ID: <6d4b89e8-452f-521e-3464-7981e89794e0@linaro.org> Date: Tue, 24 May 2022 04:48:08 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Subject: Re: Emulating CPUs with larger atomic accesses Content-Language: en-US To: Florian Weimer Cc: qemu-devel@nongnu.org References: <87k0apeor5.fsf@oldenburg.str.redhat.com> <37f4c866-4344-37ba-b64b-fd338dc96887@linaro.org> <87sfozuvpf.fsf@oldenburg.str.redhat.com> From: Richard Henderson In-Reply-To: <87sfozuvpf.fsf@oldenburg.str.redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2607:f8b0:4864:20::434; envelope-from=richard.henderson@linaro.org; helo=mail-pf1-x434.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 5/24/22 02:27, Florian Weimer wrote: > * Richard Henderson: > >> On 5/13/22 03:00, Florian Weimer wrote: >>> What's QEMU's approach to emulating CPU instructions that atomatically >>> operate on values larger than what is supported by the host CPU? >>> I assume that for full system emulation, this is not a problem, but >>> qemu-user will not achieve atomic behavior on shared memory mappings. >>> How much of a problem is this in practice? >> >> Well, it doesn't work, no. In practice, x86_64 supports 128-bit >> atomic operations, and guest requires more than that. No one really >> cares anymore about 32-bit hosts with smaller atomic operations. > > Which part doesn't work? Full-system emulation? No, user-only. > Do guests really require wider-than-128 atomics? That's quite > surprising? Typo there -- "and no guest requires...". r~