From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Campbell Subject: Re: PVHVM drivers in upstream linux kernel Date: Tue, 2 Dec 2014 11:36:15 +0000 Message-ID: <1417520175.24320.13.camel@citrix.com> References: <547D88EF.4050206@suse.com> <547D9A4A.6010201@citrix.com> <1417518314.24320.9.camel@citrix.com> <547DA392.90701@suse.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <547DA392.90701@suse.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Juergen Gross Cc: "xen-devel@lists.xensource.com" , David Vrabel List-Id: xen-devel@lists.xenproject.org On Tue, 2014-12-02 at 12:33 +0100, Juergen Gross wrote: > On 12/02/2014 12:05 PM, Ian Campbell wrote: > > On Tue, 2014-12-02 at 10:54 +0000, David Vrabel wrote: > >> On 02/12/14 09:39, Juergen Gross wrote: > >>> Hi, > >>> > >>> looking into the upstream linux sources I realized that the PVHVM > >>> drivers of XEN are only available with the pvops kernel. Is this on > >>> purpose? Shouldn't the frontend drivers, xen/platform-pci.c etc. be > >>> configurable without having to enable CONFIG_PARAVIRT? > >> > >> I suppose that would be possible but I don't think it's a useful > >> configuration because you would lose PV spinlocks for example. > > > > IIRC the reason this hasn't been implemented until now is that > > refactoring would be required to the various bits of driver code which > > assumes PAE + PARAVIRT when they aren't strictly needed, e.g. grant > > table code. Whether its worth the churn at this stage is debatable, but > > I think the (in)ability to use PV spinlocks is a red-herring. > > > > Adding PV drivers to an HVM guest is a useful thing to do, even without > > PV spinlocks. PV IO gets you far more incremental benefit than the locks > > do, adding PV IO paths is the number 1 thing which should be done to any > > guest. > > I take this as an "ack" to change this. :-) It's a best "IMHO being able to do this is a useful thing". I can't ack the actual final patch, a) I'm not a relevant maintainer and b) I've not seen the patch. > Okay, how do the current config settings regarding Xen look like? ...I'll leave the mechanics down to you and the maintainers to thrash out. Ian.