Re: [RFC PATCH v3 8/8] target/s390x: Use start-powered-off CPUState property

[Cornelia Huck <cohuck@redhat.com>]

On Tue, 28 Jul 2020 21:51:33 -0300
Thiago Jung Bauermann <bauerman@linux.ibm.com> wrote:

> Hi,
> 
> Cornelia Huck <cohuck@redhat.com> writes:
> 
> > On Wed, 22 Jul 2020 23:56:57 -0300
> > Thiago Jung Bauermann <bauerman@linux.ibm.com> wrote:
> >  
> >> Instead of setting CPUState::halted to 1 in s390_cpu_initfn(), use the
> >> start-powered-off property which makes cpu_common_reset() initialize it
> >> to 1 in common code.
> >> 
> >> Note that this changes behavior by setting cs->halted to 1 on reset, which
> >> didn't happen before.  
> >
> > I think that should be fine, as we change the cpu state to STOPPED in
> > the reset function, which sets halted to 1.  
> 
> Nice, thanks for checking.
> 
> >> 
> >> Signed-off-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>
> >> ---
> >>  target/s390x/cpu.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >> 
> >> NB: I was only able to test that this patch builds. I wasn't able to
> >> run it.  
> >
> > No noticeable difference under kvm, but running under tcg seems a bit
> > more sluggish than usual, and I saw some pausing on reboot (after the
> > bios handover to the kernel). Not sure if it were just flukes on my
> > laptop, would appreciate if someone else could give it a go.  

Experimented a bit with it again. There's a pause when switching from
the bios to the kernel (after the load reset normal has been done, I
guess), which is always there, but seems to get more noticeable with
this patch (varying wildly, but seems longer on average.) Hard to pin
down, and I don't really see a reason why that should happen, as we
should end up with halted == 1 in any case. Might still be a fluke,
even though I see it both on my laptop and on an LPAR (when running
under tcg; not seen under kvm, which is much faster anyway.)

> 
> I tried today setting up a TCG guest, but didn't have success yet.
> Will try some more tomorrow.
> 

I'm also looking a bit at the other s390 folks :)