From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753502Ab1HXVKn (ORCPT ); Wed, 24 Aug 2011 17:10:43 -0400 Received: from terminus.zytor.com ([198.137.202.10]:57829 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752116Ab1HXVKm (ORCPT ); Wed, 24 Aug 2011 17:10:42 -0400 Message-ID: <4E5568AC.2040605@zytor.com> Date: Wed, 24 Aug 2011 14:10:04 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:6.0) Gecko/20110816 Thunderbird/6.0 MIME-Version: 1.0 To: Borislav Petkov CC: Andrew Lutomirski , Al Viro , Ingo Molnar , "user-mode-linux-devel@lists.sourceforge.net" , Richard Weinberger , "linux-kernel@vger.kernel.org" , "mingo@redhat.com" Subject: Re: [uml-devel] SYSCALL, ptrace and syscall restart breakages (Re: [RFC] weird crap with vdso on uml/i386) References: <20110823010146.GY2203@ZenIV.linux.org.uk> <20110823011312.GZ2203@ZenIV.linux.org.uk> <20110823021717.GA2203@ZenIV.linux.org.uk> <20110823061531.GC2203@ZenIV.linux.org.uk> <20110823162251.GC13138@aftab> <4E53FC6E.1030807@zytor.com> <20110823205616.GA15295@aftab> <4E54163B.6080205@zytor.com> <20110823211047.GC15295@aftab> In-Reply-To: <20110823211047.GC15295@aftab> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/23/2011 02:10 PM, Borislav Petkov wrote: > On Tue, Aug 23, 2011 at 05:06:03PM -0400, H. Peter Anvin wrote: >> On 08/23/2011 01:56 PM, Borislav Petkov wrote: >>> >>> But no, I don't think the difference has disappeared - to the contrary, >>> AFAICT, the intention is for SYSCALL to be the fastest way to do >>> syscalls on x86 due to diminished number of segment checks etc. INT80 >>> is legacy, slower, etc. I believe Andy measured a similar situation on >>> Sandy Bridge with SYSCALL having latencies in the tens of nsecs range >>> and INT80 being much slower. Ingo also measured a similar situation >>> where the latency gap between the two on Intel is even bigger. >>> >> >> Sandy Bridge doesn't have SYSCALL32 at all. It has SYSENTER and SYSCALL64. > > Yeah, I was talking about SYSCALL in general. > By the way, Borislav; any way you could nudge your hardware people into a) supporting SYSENTER in compatibility mode, and b) giving us a way to turn SYSCALL *off* in compat mode? ... for future chips? -hpa