From owner-freebsd-stable@FreeBSD.ORG Fri Feb 27 18:49:11 2009 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id E15471065676; Fri, 27 Feb 2009 18:49:11 +0000 (UTC) (envelope-from alan.l.cox@gmail.com) Received: from yw-out-2324.google.com (yw-out-2324.google.com [74.125.46.28]) by mx1.freebsd.org (Postfix) with ESMTP id 80D8F8FC24; Fri, 27 Feb 2009 18:49:11 +0000 (UTC) (envelope-from alan.l.cox@gmail.com) Received: by yw-out-2324.google.com with SMTP id 2so829918ywt.13 for ; Fri, 27 Feb 2009 10:49:10 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:reply-to:in-reply-to :references:date:message-id:subject:from:to:cc:content-type; bh=7Zy3TriLO7BkdCoeo0Ttxpl5F9lKkXcDdFfmyF2PkVU=; b=noPKbuhVWPyMifTx2j8IZzKLbKg6wG7AogHoP4n1tHsfF4xeXNc86M9hikYKiQZa0P NaRUFTEQtVsYEt7G9S1D8ulJWgdYuDXpW+lOjkGd81YGPI0dXWrr4H+5eEDPeWnimuk8 tdkb9jGWdC+E9ajBTXucnVxdCb+qlnWaJGuBg= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:reply-to:in-reply-to:references:date:message-id :subject:from:to:cc:content-type; b=HQhNx6ms1nUkJvA7hW/hLfYDBUklQHa3HDV1VsDu9Iw1CuzKXZeobCQ/f7LDAkztGA tEzcZAgkr2SFsKgG5RGWSE71bp87I0Z3dFS7QpwCm1GVlW4z6xkGSbb9AMbE6mhKbPkb 9kgloRveSBI3GBtPldJe1vtH3nDeDai77WhqM= MIME-Version: 1.0 Received: by 10.151.106.7 with SMTP id i7mr4461909ybm.14.1235760550862; Fri, 27 Feb 2009 10:49:10 -0800 (PST) In-Reply-To: <200902271143.00094.jhb@freebsd.org> References: <20090227130830.GI51952@rambler-co.ru> <200902271026.15796.jhb@freebsd.org> <49A812EC.8060408@protected-networks.net> <200902271143.00094.jhb@freebsd.org> Date: Fri, 27 Feb 2009 12:49:10 -0600 Message-ID: From: Alan Cox To: John Baldwin Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Content-Filtered-By: Mailman/MimeDel 2.1.5 Cc: freebsd-stable@freebsd.org Subject: Re: 7.1-STABLE does not boot after recent superpage support MFC X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: alc@freebsd.org List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 27 Feb 2009 18:49:12 -0000 On Fri, Feb 27, 2009 at 10:42 AM, John Baldwin wrote: > On Friday 27 February 2009 11:21:00 am Michael Butler wrote: > > John Baldwin wrote: > > > On Friday 27 February 2009 8:08:30 am Igor Sysoev wrote: > > > > > >> And the message is cycled. The kernel does not boot despite > > >> vm.pmap.pg_ps_enabled value. > > > > > > This should now be fixed, apologies for the breakage. :( > > > > What are the benefits and/or impacts of enabling this? > > > > Is there anything to be gained with respect to cache and/or TLB > > utilization in allowing entry promotion through a reduced "footprint" or > > similar? How much does this depend on architecture, say, e.g. Core-2 Duo > > vs. Pentium? > > Yes there are gains due to what you mention, but it does depend on the > specific processor and specifically the how it manages entries for large > pages in its TLB (some processsors have separate TLB entries for large > pages > and have very few of them, others can store either a small or lage page in > a > single TLB slot, etc.). Alan knows far more of the details of this than I > do. > > > I note that it is not enabled by default in -current either - just > curious, > > Actually, it is enabled by default on amd64 in current. > > -- > John Baldwin > _______________________________________________ > freebsd-stable@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-stable > To unsubscribe, send any mail to "freebsd-stable-unsubscribe@freebsd.org" > The short answer is ... if you're running an amd64 kernel on a Pentium 4, Core 2, or tri- or quad-core Opteron/Phenom, enable promotion. Your results with other amd64-compatible processors, single- and dual-core Athlon/Opteron and Atom, will be application dependent. You'll win some and you'll lose some. For a longer answer with data and figures, take a look at this paper: http://ft.ornl.gov/pubs-archive/ispass-final-csmd.pdf That said, there are secondary benefits to enabling large page support that have nothing to do with the TLB, specifically, it makes fork()ing and exit()ing large address spaces cheaper. Regards, Alan