From owner-freebsd-stable@FreeBSD.ORG Mon Feb 23 20:27:05 2009 Return-Path: Delivered-To: stable@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id ADD3F10656CC; Mon, 23 Feb 2009 20:27:05 +0000 (UTC) (envelope-from rwatson@FreeBSD.org) Received: from cyrus.watson.org (cyrus.watson.org [65.122.17.42]) by mx1.freebsd.org (Postfix) with ESMTP id 829B88FC1F; Mon, 23 Feb 2009 20:27:05 +0000 (UTC) (envelope-from rwatson@FreeBSD.org) Received: from fledge.watson.org (fledge.watson.org [65.122.17.41]) by cyrus.watson.org (Postfix) with ESMTPS id 36ADC46B2A; Mon, 23 Feb 2009 15:27:05 -0500 (EST) Date: Mon, 23 Feb 2009 20:27:05 +0000 (GMT) From: Robert Watson X-X-Sender: robert@fledge.watson.org To: Maxim Sobolev In-Reply-To: <49A30456.5010400@FreeBSD.org> Message-ID: References: <200902231652.n1NGqMxH047731@post.behrens.de> <49A2DE9D.4090902@FreeBSD.org> <49A2ED6A.9040202@FreeBSD.org> <49A30456.5010400@FreeBSD.org> User-Agent: Alpine 2.00 (BSF 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Cc: Frank Behrens , Jeff Roberson , "current@freebsd.org" , stable@FreeBSD.org Subject: Re: The machdep.hyperthreading_allowed & ULE weirdness in 7.1 X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 23 Feb 2009 20:27:06 -0000 On Mon, 23 Feb 2009, Maxim Sobolev wrote: >>> Unfortunately access to BIOS is not always an option and also some BIOSes >>> don't even provide a feature to turn HTT off. >> >> It's not quite that simple -- in a world of device drivers pinning threads >> to CPUs for workload distribution, callout threads and >> sched_bind()/sched_pin() for crypto load distribution, etc, you need a >> whole infrastructure for software-disabled CPUs. Disabling it using the >> BIOS or device.hints is the only reliable way to do this right now. >> Changing the architecture of the kernel to disable CPU cores after boot is >> a significant investment of work, and as I mentioned elsewhere, it is >> disable to do this so that we can support dynamic reconfiguration in the >> presence of a hypervisor, but it's highly non-trivial. There may be some >> shortcuts that can be taken for policy reasons in the probing of CPUs when >> the topology is detected that avoid the full dynamic solution having to be >> done in the short-term, that in effect are a short-hand for device.hints >> entries, but I don't know to what extent the CPU topology from ACPI is >> available at the point where we'd need to know that. > > So, are you suggesting that we should disable machdep.hyperthreading_allowed > with ULE in 7.x and current to avoid confusion? Possibly even without ULE. Robert N M Watson Computer Laboratory University of Cambridge