From owner-cvs-all@FreeBSD.ORG Mon May 16 09:41:36 2005 Return-Path: Delivered-To: cvs-all@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id DE1F016A4CE for ; Mon, 16 May 2005 09:41:36 +0000 (GMT) Received: from mail.chesapeake.net (chesapeake.net [208.142.252.6]) by mx1.FreeBSD.org (Postfix) with ESMTP id 4F19543DA6 for ; Mon, 16 May 2005 09:41:36 +0000 (GMT) (envelope-from jroberson@chesapeake.net) Received: from mail.chesapeake.net (localhost [127.0.0.1]) by mail.chesapeake.net (8.12.10/8.12.10) with ESMTP id j4G9fN1h045730; Mon, 16 May 2005 05:41:23 -0400 (EDT) (envelope-from jroberson@chesapeake.net) Received: from localhost (jroberson@localhost)j4G9fN4x045726; Mon, 16 May 2005 05:41:23 -0400 (EDT) (envelope-from jroberson@chesapeake.net) X-Authentication-Warning: mail.chesapeake.net: jroberson owned process doing -bs Date: Mon, 16 May 2005 05:41:23 -0400 (EDT) From: Jeff Roberson To: Peter Jeremy In-Reply-To: <20050516080031.GD34537@server.vk2pj.dyndns.org> Message-ID: <20050516053818.E53620@mail.chesapeake.net> References: <97079.1116154766@critter.freebsd.dk> <4287AD84.6070600@root.org> <20050516080031.GD34537@server.vk2pj.dyndns.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII cc: src-committers@FreeBSD.org cc: Jacques Vidrine cc: cvs-src@FreeBSD.org cc: cvs-all@FreeBSD.org cc: Poul-Henning Kamp cc: Colin Percival cc: Nate Lawson Subject: Re: cvs commit: src/sys/amd64/amd64mp_machdep.csrc/sys/amd64/include cpufunc.h src/sys/i386/i386 mp_machdep.c src/sys/i386/include cpufunc.h X-BeenThere: cvs-all@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: CVS commit messages for the entire tree List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 16 May 2005 09:41:37 -0000 On Mon, 16 May 2005, Peter Jeremy wrote: > On Sun, May 15, 2005 at 01:13:56PM -0700, Nate Lawson wrote: > >My point was that FreeBSD (like most general-purpose OS) has many timing > >channels that are comparably as effective for an attacker as HTT. > > If you take the bandwidth of the timing channel into account, I don't > believe there are any other timing channels that come anywhere near the > HTT attack. Maybe Colin has a better idea of what other timing channels > exist and how they compare to HTT. > > >Disabling HTT does not significantly reduce an attacker's likelihood of > >success since they can just use another timing channel. However, it > >does disable a useful feature. Are we going to disable SMP next? > > How useful is HTT on FreeBSD? FreeBSD does not have a HTT-aware > scheduler at present and I don't believe there are even any plans to > make either scheduler HTT-aware. Without this, you only gain a benefit > if you are running fairly specific workloads. The statement about schedulers is not entirely true. ULE has lots of special case code for HTT, and 4bsd even has a small amount. In any event it's hard to prevent general purpose workloads from slowing down with htt. At one point ule was certainly as fast with htt as without, but I believe there are many bugs that prevent us from taking real measurements at the moment. Long term for HTT, if intel keeps it implemented the way it is now, I was intending to only schedule threads from the same process on the second core. I believe this would leave it as an optimization which will only effect the few cases that it is likely to help. Anyway, I am not going to throw in my .02 on whether or not it should be disabled, but I will say that both schedulers have some awareness of htt. > > Peter >