[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] PVHVM drivers in upstream linux kernel
On Tue, Dec 02, 2014 at 11:05:14AM +0000, 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. > > One actual usecase is installing from a distro installer which isn't > PAE, let alone PARAVIRT enabled[0], to get far enough that you can > install a more capable PVHVM kernel with more bells and whistles. > > If there were distros around who refused wholesale to enable PARAVIRT > even in a non-default kernel then it would be more likely that they > could be convinced to enable a set of PV IO drivers, since they have 0 > impact on a non-PARAVIRT system, and still give significant benefit to > Xen users. I don't know of any of the major distros are refusing > PARAVIRT in this way though. > > Ian. > > [0] The default i386 Debian installer falls into this camp, but you can > use the special PV Xen variant to install as PVHVM too so it's not so > critical. And the Fedora 21 LiveISO (32-bit) does too. > > > _______________________________________________ > Xen-devel mailing list > Xen-devel@xxxxxxxxxxxxx > http://lists.xen.org/xen-devel _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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