[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] PVHVM drivers in upstream linux kernel
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. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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