From mboxrd@z Thu Jan 1 00:00:00 1970 From: "H. Peter Anvin" Subject: Re: [PATCH 0/7] preempt_count rework -v2 Date: Wed, 11 Sep 2013 09:00:30 -0700 Message-ID: <5230939E.3050408@zytor.com> References: <20130910130811.507933095@infradead.org> <20130910135152.GD7537@gmail.com> <20130910135636.GA8268@gmail.com> <522F3ACC.9000701@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: Received: from terminus.zytor.com ([198.137.202.10]:53051 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755159Ab3IKQBs (ORCPT ); Wed, 11 Sep 2013 12:01:48 -0400 In-Reply-To: Sender: linux-arch-owner@vger.kernel.org List-ID: To: Linus Torvalds Cc: Arjan van de Ven , Ingo Molnar , Peter Zijlstra , Andi Kleen , Mike Galbraith , Thomas Gleixner , Frederic Weisbecker , Linux Kernel Mailing List , "linux-arch@vger.kernel.org" On 09/10/2013 09:24 AM, Linus Torvalds wrote: > On Tue, Sep 10, 2013 at 8:29 AM, Arjan van de Ven wrote: >>> >> also.. yuck on using "dec" >> "dec" sucks, please use "sub foo ,1" instead > > That's a bigger instruction, largely due to the constant. > >> (dec sucks because of its broken flags behavior; it creates basically a >> bubble in the pipeline) > > Intel could (and should) just fix that. It's "easy" enough - you just > need to rename the carry flag as a separate register (and make sure > that the conditional instructions that don't use it don't think they > need it). > > In fact I thought Intel already did that on their large cores. Are you > sure they still have trouble with inc/dec? > Big cores are fine, but Atom (and presumably Quark) might still suffer a performance penalty. -hpa