From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-ed1-f42.google.com (mail-ed1-f42.google.com [209.85.208.42]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8983112E1FE for ; Thu, 7 Mar 2024 18:18:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.208.42 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709835534; cv=none; b=b6qomTq0f0qO526kk/19mLap5IJU8tlA09s3TF5k1Szwcu3S6ju+02w/KVMtGEFWAMktpqocMj5NHfKA+DWu00lxmKG5dwjr08j+qq+wdBIRPTFrrC8ZQ9fxxjQoRd06N4GAIaA8s7PwnxKFik0xy42VkKL8jNQ3MQFBZiQU1Y4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709835534; c=relaxed/simple; bh=FXT4m7HmrVbNlkkcuqc4h5hIuOLr2Owzoeu7EYph2QU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=MWHv+bCbRSoAfJ0RxbrpjSe+yW+vFRBsBOvM/08eHovSm51TzcEYqiccoiobAGudd01jodWeAZ3imR6fazI0F8BvqzcYERzuWsUSqHl9aOa6PfZ4NSrBJfVeXlp5WqnVOTDTgqcXsEbf4kEIkj+/SCBHNhPcXkGmaskBbByq0o4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=ebOeCamR; arc=none smtp.client-ip=209.85.208.42 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="ebOeCamR" Received: by mail-ed1-f42.google.com with SMTP id 4fb4d7f45d1cf-56647babfe6so1800985a12.3 for ; Thu, 07 Mar 2024 10:18:52 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1709835531; x=1710440331; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=3ih2qp0TpnzVvtyG5Tp6Nj5YhfoLGtJWPyIG/4IO+Lc=; b=ebOeCamRvZrgmoWb23Ekh1qyArb9pieXzv1tZdVn5IWgXSdHUZJT4uR2iq7Ac/HFXm m3P7nJu17yBLx6g+oLgWjhRCDpQIgpNLm1tqbEK21hsjxlO9YDsRX0rPBOZUdgkLxAnI fm/oO69JAmB/rMWcHxIER3gKmzBtXbWhVhGIvOm4juKiQ5TjFLF6h/kManun44OVDI9K QS70izlgCjqBTU3RUl1M/kGWBM0Etkq5MCfQhxZCsI1yLV13Bb6D2NDAPrpr2xQsWv+J 2B0F17Z1vsOKOZOuO7nTWxuMFOCD9oa72rl6I8IqtwWWEw63P4nKMMdZvPROWFBFoCQX KuJQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1709835531; x=1710440331; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=3ih2qp0TpnzVvtyG5Tp6Nj5YhfoLGtJWPyIG/4IO+Lc=; b=uwugJhWKtDHkaIv7a39vkNf+j3/UezH9cCvBx9Bq3HcmpxVIlI6erTLs9/+dEyrM34 pxWr0yFiYRLzrU3Eb37QKO/bZjtyd4qvj9TmvsdILXIM3MMZtJr7CiRNDGKiHXx1yTvj Q1uryECY3egBgk9OLRrNShQJm/rj0D0jC4vu59RH54NqpDHorzqVphL+bLDHzpmnja6C uiBG471Axx3c1w2gO7+aXplkQrAgvSZhVzgBQPVrGVYcNdi99X8BftDwNaUO0VsxFKQ5 OAu0Ab0gKUg3+A+hRJZ4MI7wkSCQH/xXmRMlFr9lbOCANQJA3US01GUhnl6SefyXjuih a2Ag== X-Forwarded-Encrypted: i=1; AJvYcCU5es+9+38C1oBfZ+Xwh4P/QaRoriHgq5H9tm29G9qYRhUoAtOCP8WwOvX7RaW7Vpcd57ecEFG7smaVNRKr1+aYyk3RvutpBhxgBQN+ X-Gm-Message-State: AOJu0YxWtzGMWRS581HBinvVrTykM0iE76rWfdt7a3lH0+bQXowGtKws nVwYVRUYUAf82GUlu/KVbh4J5aUeQ2n4HLAamn879zeBZWAj5IPIUQkN4Ftb X-Google-Smtp-Source: AGHT+IFjVyBM1I0YrYvFS2Yf7mFCSmMnGCqlE5FTKQWqn6ZXKlyaKeLTlmjxtg3EWaKCaHD5DH9Spw== X-Received: by 2002:a17:906:f8c8:b0:a45:20e3:688e with SMTP id lh8-20020a170906f8c800b00a4520e3688emr8941380ejb.56.1709835530603; Thu, 07 Mar 2024 10:18:50 -0800 (PST) Received: from andrea ([31.189.122.3]) by smtp.gmail.com with ESMTPSA id lk11-20020a170906cb0b00b00a4577ffe69csm4137062ejb.78.2024.03.07.10.18.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 07 Mar 2024 10:18:50 -0800 (PST) Date: Thu, 7 Mar 2024 19:18:46 +0100 From: Andrea Parri To: Alan Stern Cc: Kenneth-Lee-2012@foxmail.com, linux-kernel@vger.kernel.org, paulmck@kernel.org Subject: Re: Question about PB rule of LKMM Message-ID: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: > So I guess you're talking about the second, intuitive meaning. That's > very simple to explain. Since every instruction executes at _some_ > time, and since we can safely assume that no two instructions execute at > exactly the _same_ time, if F doesn't execute before E then E must > execute before F. Or using your terms, (not F ->xb E) implies (E ->xb > F). Would that answer the original question satisfactorily? I'd disagree with these premises: certain instructions can and do execute at the same time. FWIW, in the formal model, it is not that difficult to provide examples of "(not F ->xb E) and (not E ->xb F)". > The new text says the same thing as the original, just in a more > condensed way. It skips the detailed explanation of why E must execute > before W propagates to E's CPU, merely saying that it is because "W is > coherence-later than E". I'm not sure this is an improvement; the > reader might want to know exactly how this reasoning goes. The current text relies on an argument by contradiction. A contradiction is reached by "forcing" (F ->xb E), hence all it can be concluded is that (not F ->xb E). Again, AFAICS, this doesn't match the claim in the text. Andrea