From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx133.postini.com [74.125.245.133]) by kanga.kvack.org (Postfix) with SMTP id 1A5B16B004D for ; Mon, 30 Jul 2012 15:21:51 -0400 (EDT) Date: Mon, 30 Jul 2012 20:21:40 +0100 From: Jamie Lokier Subject: Re: [RFC] page-table walkers vs memory order Message-ID: <20120730192140.GU25459@jl-vm1.vm.bytemark.co.uk> References: <1343064870.26034.23.camel@twins> <20120725175628.GH2378@linux.vnet.ibm.com> <20120725211217.GR2378@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120725211217.GR2378@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: "Paul E. McKenney" Cc: Hugh Dickins , Peter Zijlstra , Linus Torvalds , Rik van Riel , Andrew Morton , Nick Piggin , Andrea Arcangeli , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org Paul E. McKenney wrote: > > Does some version of gcc, under the options which we insist upon, > > make such optimizations on any of the architectures which we support? > > Pretty much any production-quality compiler will do double-fetch > and old-value-reuse optimizations, the former especially on 32-bit > x86. I don't know of any production-quality compilers that do value > speculation, which would make the compiler act like DEC Alpha hardware, > and I would hope that if this does appear, (1) we would have warning > and (2) it could be turned off. But there has been a lot of work on > this topic, so we would be foolish to rule it out. GCC documentation for IA-64: -msched-ar-data-spec -mno-sched-ar-data-spec (En/Dis)able data speculative scheduling after reload. This results in generation of ld.a instructions and the corresponding check instructions (ld.c / chk.a). The default is 'enable'. I don't know if that results in value speculation of the relevant kind. -- Jamie -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org