Re: [qemu-s390x] [Qemu-devel] [PATCH] S390: Expose s390-specific CPU info

[Cornelia Huck]

On Thu, 8 Feb 2018 09:09:04 -0500
Luiz Capitulino <address@hidden> wrote:

> On Thu,  8 Feb 2018 10:48:08 +0100
> Viktor Mihajlovski <address@hidden> wrote:
> 
> > Presently s390x is the only architecture not exposing specific
> > CPU information via QMP query-cpus. Upstream discussion has shown
> > that it could make sense to report the architecture specific CPU
> > state, e.g. to detect that a CPU has been stopped.  
> 
> I'd very strongly advise against extending query-cpus. Note that the
> latency problems with query-cpus exists in all archs, it's just a
> matter of time for it to pop up for s390 use-cases too.
> 
> I think there's three options for this change:
> 
>  1. If this doesn't require interrupting vCPU threads, then you
>     could rebase this on top of query-cpus-fast

From my perspective, rebasing on top of query-cpus-fast looks like a
good idea. This would imply that we need architecture-specific fields
for the new interface as well, though.

> 
>  2. If you plan to keep adding s390 state/registers to QMP commands,
>     then you could consider adding a query-s390-cpu-state or add
>     a query-cpu-state command that accepts the arch name as a parameter

Personally, I don't see a need for more fields. But maybe I'm just
unimaginative.

> 
>  3. If you end up needing to expose state that actually needs an
>     ioctl, then we should consider porting info registers to QMP
> 
> > 
> > With this change the output of query-cpus will look like this on
> > s390:
> > 
> >     [{"arch": "s390", "current": true,
> >       "props": {"core-id": 0}, "cpu_state": "operating", "CPU": 0,
> >       "qom_path": "/machine/unattached/device[0]",
> >       "halted": false, "thread_id": 63115},
> >      {"arch": "s390", "current": false,
> >       "props": {"core-id": 1}, "cpu_state": "stopped", "CPU": 1,
> >       "qom_path": "/machine/unattached/device[1]",
> >       "halted": true, "thread_id": 63116}]
> > 
> > Signed-off-by: Viktor Mihajlovski <address@hidden>