From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [RFC][PATCH 0/5] arch: atomic rework Date: Tue, 18 Feb 2014 09:17:46 -0800 Message-ID: <20140218171746.GQ4250@linux.vnet.ibm.com> References: <20140218145645.GK4250@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from e37.co.us.ibm.com ([32.97.110.158]:34963 "EHLO e37.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751855AbaBRRRw (ORCPT ); Tue, 18 Feb 2014 12:17:52 -0500 Received: from /spool/local by e37.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 18 Feb 2014 10:17:52 -0700 Content-Disposition: inline In-Reply-To: Sender: linux-arch-owner@vger.kernel.org List-ID: To: Mark Batty Cc: Peter Sewell , peterz@infradead.org, Torvald Riegel , torvalds@linux-foundation.org, Will Deacon , Ramana.Radhakrishnan@arm.com, dhowells@redhat.com, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, mingo@kernel.org, gcc@gcc.gnu.org On Tue, Feb 18, 2014 at 03:16:33PM +0000, Mark Batty wrote: > Hi Paul, > > Thanks for the document. I'm looking forward to reading the bits about > dependency chains in Linux. And I am looking forward to your thoughts on those bits! > > One point of confusion for me... Example 4 says "language must allow". > > Shouldn't that be "language is permitted to allow"? > > When we say "allow", we mean that the optimised execution should be > allowed by the specification, and Implicitly, the unoptimised > execution should remain allowed too. We want to be concrete about what > the language specification allows, and that's why we say "must". It is > not to disallow the unoptimised execution. OK, got it! Thanx, Paul > > Seems like an > > implementation is always within its rights to avoid an optimization if > > its implementation prevents it from safely detecting the oppportunity > > for that optimization. > > That's right. > > - Mark > > > > Or am I missing something here? > > > > Thanx, Paul > > >