From owner-freebsd-xen@FreeBSD.ORG Wed Jul 6 23:55:37 2011 Return-Path: Delivered-To: freebsd-xen@freebsd.org Received: from mx2.freebsd.org (mx2.freebsd.org [IPv6:2001:4f8:fff6::35]) by hub.freebsd.org (Postfix) with ESMTP id AF2BD1065672 for ; Wed, 6 Jul 2011 23:55:37 +0000 (UTC) (envelope-from cperciva@freebsd.org) Received: from xps.daemonology.net (freefall.freebsd.org [IPv6:2001:4f8:fff6::28]) by mx2.freebsd.org (Postfix) with SMTP id 59A88151A84 for ; Wed, 6 Jul 2011 23:55:37 +0000 (UTC) Received: (qmail 19037 invoked from network); 6 Jul 2011 23:55:36 -0000 Received: from unknown (HELO xps.daemonology.net) (127.0.0.1) by localhost with SMTP; 6 Jul 2011 23:55:36 -0000 Message-ID: <4E14F5F8.7080108@freebsd.org> Date: Wed, 06 Jul 2011 16:55:36 -0700 From: Colin Percival User-Agent: Mozilla/5.0 (X11; U; FreeBSD amd64; en-US; rv:1.9.1.16) Gecko/20101220 Thunderbird/3.0.11 MIME-Version: 1.0 To: gibbs@freebsd.org References: <4DF18EE5.5090704@freebsd.org> <4DF27EFF.5060005@FreeBSD.org> <4E13B6E9.9070202@freebsd.org> <4E13C2A4.5040202@FreeBSD.org> <4E13CB8F.8000009@freebsd.org> <4E13E111.9070005@freebsd.org> <4E14E7D2.9040708@FreeBSD.org> In-Reply-To: <4E14E7D2.9040708@FreeBSD.org> X-Enigmail-Version: 1.0.1 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: "freebsd-xen@freebsd.org" Subject: Re: breakage in blkfront with ring_pages > 1 X-BeenThere: freebsd-xen@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussion of the freebsd port to xen - implementation and usage List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 06 Jul 2011 23:55:37 -0000 On 07/06/11 15:55, Justin T. Gibbs wrote: > On 7/5/11 10:14 PM, Colin Percival wrote: >> On 07/05/11 19:42, Colin Percival wrote: >>> Yep. Mess or not, shall I go ahead with having a loader tunable > control this, >>> or can you think of a better solution? >> >> Does anyone object to the attached patch? It keeps the differing > behaviour to >> a minimum -- we MUST set ring-ref with a FreeBSD blkback, and we MUST > NOT set >> it with a linux blkback -- but otherwise errs in the direction of > setting more >> variables than are needed, to maximize the possibility of a future blkback >> being compatible with both blkback_is_linux=0 and blkback_is_linux=1. > > It would be better to just change the FreeBSD blkback driver to be > compatible with the RedHat convention. Fine with me, but that will of course break compatibility between pre- and post- patch versions of FreeBSD. Aside from you, how many people use the FreeBSD blkback driver? > I'm still unclear on why the current FreeBSD blkfront driver believes > that it can use more than one page in your configuration given that the > RedHat blkfront doesn't advertise this capability in a way that the FreeBSD > blkfront understands (max-ring-pages isn'te set by blkback). Did you do > something to force blkfront to use more than one page? I'm seeing max-ring-pages set to 4. I don't know what tree EC2 is using on their Dom0 -- I've heard rumours that there's a lot of RedHat going on behind the scenes, but given Amazon's size it's entirely possible that they got a blkback which hasn't been released publicly. I'm sent an email asking where their blkback came from; I'll report back if/when I know something. -- Colin Percival Security Officer, FreeBSD | freebsd.org | The power to serve Founder / author, Tarsnap | tarsnap.com | Online backups for the truly paranoid