From owner-freebsd-current@FreeBSD.ORG Tue Feb 28 22:18:17 2012 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id D870D1065679; Tue, 28 Feb 2012 22:18:17 +0000 (UTC) (envelope-from kob6558@gmail.com) Received: from mail-wi0-f182.google.com (mail-wi0-f182.google.com [209.85.212.182]) by mx1.freebsd.org (Postfix) with ESMTP id 4091F8FC1C; Tue, 28 Feb 2012 22:18:17 +0000 (UTC) Received: by wibhn6 with SMTP id hn6so2507874wib.13 for ; Tue, 28 Feb 2012 14:18:16 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; bh=AmsLtio9N0XQs5WvJ44J44mXPYXUeSIQobxG97KZDpc=; b=nm4J5MBlscU7/KRIuDuadtFsuJlpQtsP3g92rVPJURj+LH0X6eA+teEewITrTebY69 DQJlqIkbF8lKQhNLaOH7Rxe+8GsxO1w2uxhZ5EvcAgp9ysLl1ZU9bie3xXSfxzg+P427 L5EaFJVyND3IzjZ44ZBi4bQGt0lEbd/Q27bzs= MIME-Version: 1.0 Received: by 10.216.135.102 with SMTP id t80mr5065046wei.59.1330467496354; Tue, 28 Feb 2012 14:18:16 -0800 (PST) Received: by 10.223.16.82 with HTTP; Tue, 28 Feb 2012 14:18:16 -0800 (PST) In-Reply-To: <3BA1B476-ED05-4E8E-8DFA-0B06EFB48867@samsco.org> References: <4F26CC5A.2070501@FreeBSD.org> <4F4B5ED3.5090508@FreeBSD.org> <65B1891F-9079-4948-BF37-8A50B4E85071@samsco.org> <4F4C0600.2000903@FreeBSD.org> <3BA1B476-ED05-4E8E-8DFA-0B06EFB48867@samsco.org> Date: Tue, 28 Feb 2012 14:18:16 -0800 Message-ID: From: Kevin Oberman To: Scott Long Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Cc: FreeBSD current , Devin Teske , Andriy Gapon Subject: Re: revisiting tunables under Safe Mode menu option X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 28 Feb 2012 22:18:17 -0000 On Mon, Feb 27, 2012 at 10:23 PM, Scott Long wrote: > > On Feb 27, 2012, at 3:38 PM, Andriy Gapon wrote: >>> >>> Turning off the APIC turns off SMP in a very efficient, clean manner. = =A0I >>> added this not to isolate the APIC code, but to turn off SMP. =A0That's= why >>> it's there, and I'd like the ability to turn off SMP to stay there in s= ome >>> form. >> >> I think that this is a good idea. >> >>> If there's a better way to disable SMP that doesn't get into problems >>> with interrupt delivery, then please propose it. >> >> I think that kern.smp.disabled should be it. >> > > I recall this tunable being problematic, but I don't recall the reason. = =A0Reading the code > makes me think that it should be fine; maybe it's time to switch this kno= b from > hint.apic.0.disabled to kern.smp.disabled, as you've done in your propose= d patch. APIC is required for SMP, but works on many older, single CPU systems and removes the massive sharing of IRQs common on non-APIC systems. OTOH, some ThinkPads simply won't boot with APIC. My old T43 (Pentium-M) had this issue. I had to turn off APIC to get a GENERIC kernel to boot. I think that I have heard of other systems that have an issue with FreeBSD APIC. (APIC seems to work fine with Windows, so it's something about the FreeBSD implementation, but the problem is pretty rare, seems limited to 3-5 year old uniprocessor systems, so it's probably not worth trying to track down. --=20 R. Kevin Oberman, Network Engineer E-mail: kob6558@gmail.com