Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262805AbVENQcq (ORCPT ); Sat, 14 May 2005 12:32:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262799AbVENQbO (ORCPT ); Sat, 14 May 2005 12:31:14 -0400 Received: from mustang.oldcity.dca.net ([216.158.38.3]:59582 "HELO mustang.oldcity.dca.net") by vger.kernel.org with SMTP id S262800AbVENQab (ORCPT ); Sat, 14 May 2005 12:30:31 -0400 Subject: Re: Hyper-Threading Vulnerability From: Lee Revell To: Alan Cox Cc: Dave Jones , Matt Mackall , Andy Isaacson , Andi Kleen , "Richard F. Rebel" , Gabor MICSKO , Linux Kernel Mailing List , tytso@mit.edu In-Reply-To: <1116084186.20545.47.camel@localhost.localdomain> References: <1115963481.1723.3.camel@alderaan.trey.hu> <1116009483.4689.803.camel@rebel.corp.whenu.com> <20050513190549.GB47131@muc.de> <20050513212620.GA12522@hexapodia.org> <20050513215905.GY5914@waste.org> <1116024419.20646.41.camel@localhost.localdomain> <1116025212.6380.50.camel@mindpipe> <20050513232708.GC13846@redhat.com> <1116027488.6380.55.camel@mindpipe> <1116084186.20545.47.camel@localhost.localdomain> Content-Type: text/plain Date: Sat, 14 May 2005 12:30:28 -0400 Message-Id: <1116088229.8880.7.camel@mindpipe> Mime-Version: 1.0 X-Mailer: Evolution 2.3.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1287 Lines: 27 On Sat, 2005-05-14 at 16:23 +0100, Alan Cox wrote: > On Sad, 2005-05-14 at 00:38, Lee Revell wrote: > > Well yes but you would still have to recompile those apps. And take the > > big performance hit from using gettimeofday vs rdtsc. Disabling HT by > > default looks pretty good by comparison. > > You cannot use rdtsc for anything but rough instruction timing. The > timers for different processors run at different speeds on some SMP > systems, the timer rates vary as processors change clock rate nowdays. > Rdtsc may also jump dramatically on a suspend/resume. > > If the app uses rdtsc then generally speaking its terminally broken. The > only exception is some profiling tools. That is basically all JACK and mplayer use it for. They have RT constraints and the tsc is used to know if we got woken up too late and should just drop some frames. The developers are aware of the issues with rdtsc and have chosen to use it anyway because these apps need every ounce of CPU and cannot tolerate the overhead of gettimeofday(). Lee - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/