Re: [Qemu-devel] [PATCH 03/10] target-i386: move hyperv_* static globals to CPUState

[Eduardo Habkost]

On Tue, Feb 26, 2013 at 05:12:21PM +0100, Igor Mammedov wrote:
> On Tue, 26 Feb 2013 13:01:12 -0300
> Eduardo Habkost <address@hidden> wrote:
> 
> > On Tue, Feb 26, 2013 at 04:42:17PM +0100, Igor Mammedov wrote:
> > > On Tue, 26 Feb 2013 11:50:23 -0300
> > > Eduardo Habkost <address@hidden> wrote:
> > > 
> > > > On Mon, Feb 25, 2013 at 02:03:02AM +0100, Igor Mammedov wrote:
> > > > > - since hyperv_* helper functions are used only in target-i386/kvm.c
> > > > >   move them there as static helpers
> > > > > 
> > > > > Signed-off-by: Igor Mammedov <address@hidden>
> > > > > Requestd-By: Eduardo Habkost <address@hidden>
> > > > 
> > > > I wonder if we could do this later, to make review and testing easier.
> > > > We could simply keep the hv_* handling inside parse_featurestr() by now.
> > > > I don't think this would block any of the CPU hotplug or CPU model
> > > > probing/compatibility/reliability work we're doing. I mean:
> > > device_add from CPU hot-add POV would be usable once we have all features
> > > accepted on -cpu converted to properties + sub-classes.
> > 
> > If we keep hv_* as special cases inside parse_featurestr() (the way they
> > already are), CPU hotplug should still work perfectly. I don't see why
> > it would block it.
> > 
> > 
> > > 
> > > > 
> > > > * I don't expect hv-* to appear on a machine-type compat_props array in
> > > >   the near feature.
> > > > * I don't expect people to need to set per-CPU hv-* properties on
> > > >   device_add for CPU hotplug.
> > > > 
> > > > So we could keep them as special cases on parse_featurestr(), and
> > > > convert them to per-CPU properties only after we have the subclasses and
> > > > CPU hotplug working.
> > > it won't be a consistent interface, where user who has 
> > > "-cpu XXX,+foo1,+hv_spinlocks,+foo2" on cmd-line
> > > would have to use "device_add XXX,foo1=true,foo2=true" manually excluding
> > > options from device_add, i.e. it propagates special casing to users as
> > > well. And when hv_ are moved to per-CPU fields, it might break users since
> > > they will still exclude some options.
> > 
> > Won't -cpu/parse_featurestr() simply set global properties? In this
> > case, the common case would be to call "device_add XXX" with no extra
> > options at all, so there's no option to be excluded and no special case
> > to care about.
> That is if global properties will made to 1.5  which I highly doubt taking in
> account how fast patches are reviewed and accepted. Otherwise release would
> be broken. 

IMO it _has_ to make 1.5 and is a requirement to make device_add usable
for CPU hotplug. Otherwise we would have to change the behavior of -cpu
+ device_add in an incompatible way.


> 
> > 
> > 
> > > > 
> > > > Considering that -cpu options will be translated to global properties,
> > > > it will be trivial to keep compatibility with existing behavior of "-cpu
> > > > hv_*=..." once we change them from static variables to per-CPU fields.
> > > Global properties would just allow not to specify foo1,foo2 on
> > > device_add from hot-plug POV.
> > > 
> > > If this and following patch are to complex we could fallback to
> > > alternative from v6 for hv_* features, which produce the same external
> > > property interface just with different internal approach.
> > 
> > No, v6 exposes completely different (and unexpected) semantics. It
> > exposes a per-CPU property that affects all CPU objects when it gets
> > changed.
> Do you know any guest that will work with mixed CPUs that have and doesn't
> have hv_* set at the same time?

I don't know and I don't care. But in either case you are introducing a
per-CPU QOM property for it. If it is a per-CPU QOM property, it just
makes sense that it will affect only the CPU object being changed.

What I am proposing is to make it a per-CPU QOM property only after we
make it really per-CPU, so we don't introduce weird externally-visible
property semantics that are likely to change in the near future.


> 
> > > 
> > > > 
> > > > > ---
> > > > >  target-i386/Makefile.objs |    2 +-
> > > > >  target-i386/cpu.c         |   16 +++++++---
> > > > >  target-i386/cpu.h         |    7 +++++
> > > > >  target-i386/hyperv.c      |   64
> > > > > --------------------------------------------- target-i386/hyperv.h
> > > > > |   45 ------------------------------- target-i386/kvm.c         |
> > > > > 36 ++++++++++++++++++------- 6 files changed, 45 insertions(+), 125
> > > > > deletions(-) delete mode 100644 target-i386/hyperv.c
> > > > >  delete mode 100644 target-i386/hyperv.h
> > > > > 
> > > > [...]
> > > > 
> > > 
> > > 
> > 
> 

-- 
Eduardo