Re: [Qemu-devel] [PATCH v4 11/21] s390x: allow only 1 CPU with TCG

[Cornelia Huck <cohuck@redhat.com>]

On Wed, 13 Sep 2017 14:10:53 +0200
David Hildenbrand <david@redhat.com> wrote:

> On 13.09.2017 09:19, Igor Mammedov wrote:
> > On Tue, 12 Sep 2017 17:42:35 +0200
> > David Hildenbrand <david@redhat.com> wrote:
> >   
> >> On 12.09.2017 14:43, Igor Mammedov wrote:  
> >>> On Mon, 11 Sep 2017 17:21:40 +0200
> >>> David Hildenbrand <david@redhat.com> wrote:
> >>>     
> >>>> Specifying more than 1 CPU (e.g. -smp 5) leads to SIGP errors (the
> >>>> guest tries to bring these CPUs up but fails), because we don't support
> >>>> multiple CPUs on s390x under TCG.
> >>>>
> >>>> Let's bail out if more than 1 is specified, so we don't raise people's
> >>>> hope. Make it a define, so we can easily bump it up later.
> >>>>
> >>>> Tested-by: Matthew Rosato <mjrosato@linux.vnet.ibm.com>
> >>>> Signed-off-by: David Hildenbrand <david@redhat.com>
> >>>> ---
> >>>>  hw/s390x/s390-virtio-ccw.c | 10 ++++++++++
> >>>>  1 file changed, 10 insertions(+)
> >>>>
> >>>> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
> >>>> index f67b4b5d58..f1198b2745 100644
> >>>> --- a/hw/s390x/s390-virtio-ccw.c
> >>>> +++ b/hw/s390x/s390-virtio-ccw.c
> >>>> @@ -23,6 +23,7 @@
> >>>>  #include "hw/s390x/css.h"
> >>>>  #include "virtio-ccw.h"
> >>>>  #include "qemu/config-file.h"
> >>>> +#include "qemu/error-report.h"
> >>>>  #include "s390-pci-bus.h"
> >>>>  #include "hw/s390x/storage-keys.h"
> >>>>  #include "hw/s390x/storage-attributes.h"
> >>>> @@ -47,6 +48,8 @@ S390CPU *s390_cpu_addr2state(uint16_t cpu_addr)
> >>>>      return cpu_states[cpu_addr];
> >>>>  }
> >>>>  
> >>>> +/* #define S390_TCG_SMP_SUPPORT */    
> >>> I'd drop define and ifdef for something that doesn't exists    
> >>
> >> Conny requested it as we might see some work on that area (supporting
> >> smp) soon. So as long as there are no other opinions, I'll stick to the
> >> current version.
> >>
> >> Thanks!
> >>  
> > I've just removed a bunch of TODO cpu models in PPC with
> > corresponding macro, my guess they were also introduced
> > with similar intent but ended up as dead code.
> > 
> > So it's better to add new code when it actually is needed,
> > instead of just in case.
> >   
> v1 of this patch had no ifdef at all. So I'll let Conny decide whether
> to keep it like this or whether to drop the ifdef again.

You could add a comment? OTOH, this one hits immediately, so whoever
implements smp for tcg will remember to change this :)

So no real objection to leaving out the ifdef.