From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: mips octeon memory model questions Date: Tue, 4 Feb 2014 20:05:35 +0100 Message-ID: <20140204190535.GC5002@laptop.programming.kicks-ass.net> References: <20140204184150.GB5002@laptop.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-subscribe: List-owner: List-post: List-archive: To: Linus Torvalds Cc: David Daney , Ralf Baechle , "linux-arch@vger.kernel.org" , linux-mips , Linux Kernel Mailing List , Paul McKenney , Will Deacon List-Id: linux-arch.vger.kernel.org On Tue, Feb 04, 2014 at 10:58:40AM -0800, Linus Torvalds wrote: > On Tue, Feb 4, 2014 at 10:41 AM, Peter Zijlstra wrote: > > > > Still doesn't make sense, because if we need the first sync to stop > > writes from being re-ordered with the ll-sc, we also need the second > > sync to avoid the same. > > Presumably octeon doesn't do speculative writes, only *buffered* writes. Speculative writes are bad.. :-) > So writes move down, not up. Right, but the ll-sc store might move down over a later store. Say because the ll-sc needs to first get exclusive ownership of the cacheline where the later store would be to an already owned line. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from merlin.infradead.org ([205.233.59.134]:55165 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751357AbaBDTGA (ORCPT ); Tue, 4 Feb 2014 14:06:00 -0500 Date: Tue, 4 Feb 2014 20:05:35 +0100 From: Peter Zijlstra Subject: Re: mips octeon memory model questions Message-ID: <20140204190535.GC5002@laptop.programming.kicks-ass.net> References: <20140204184150.GB5002@laptop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-arch-owner@vger.kernel.org List-ID: To: Linus Torvalds Cc: David Daney , Ralf Baechle , "linux-arch@vger.kernel.org" , linux-mips , Linux Kernel Mailing List , Paul McKenney , Will Deacon Message-ID: <20140204190535.BU88cknQJXmOa7naLEMqmWUJc2p1CAKX7W9Aes14Nhw@z> On Tue, Feb 04, 2014 at 10:58:40AM -0800, Linus Torvalds wrote: > On Tue, Feb 4, 2014 at 10:41 AM, Peter Zijlstra wrote: > > > > Still doesn't make sense, because if we need the first sync to stop > > writes from being re-ordered with the ll-sc, we also need the second > > sync to avoid the same. > > Presumably octeon doesn't do speculative writes, only *buffered* writes. Speculative writes are bad.. :-) > So writes move down, not up. Right, but the ll-sc store might move down over a later store. Say because the ll-sc needs to first get exclusive ownership of the cacheline where the later store would be to an already owned line.