Re: [Qemu-devel] [qemu-s390x] [PATCH v2 1/2] vfio-ccw: add force unlimited prefetch property

[Cornelia Huck <cohuck@redhat.com>]

On Wed, 23 May 2018 19:28:31 +0200
Halil Pasic <pasic@linux.ibm.com> wrote:

> On 05/23/2018 06:59 PM, Cornelia Huck wrote:
> > On Wed, 23 May 2018 18:23:44 +0200
> > Halil Pasic <pasic@linux.ibm.com> wrote:
> >   
> >> On 05/23/2018 04:46 PM, Cornelia Huck wrote:  
> >>>>>> +    if (!(sch->orb.ctrl0 & ORB_CTRL0_MASK_PFCH)) {
> >>>>>> +        if (!(vcdev->force_orb_pfch)) {
> >>>>>> +            warn_report("vfio-ccw requires PFCH flag set");
> >>>>>> +            sch_gen_unit_exception(sch);
> >>>>>> +            css_inject_io_interrupt(sch);
> >>>>>> +            return IOINST_CC_EXPECTED;
> >>>>>> +        } else {
> >>>>>> +            sch->orb.ctrl0 |= ORB_CTRL0_MASK_PFCH;
> >>>>>> +            WARN_ONCE(vcdev->warned_force_orb_pfch, "PFCH flag forced");  
> >>>>> This message should probably mention vfio-ccw as well as the subchannel
> >>>>> id?
> >>>>>         
> >>>> I was thinking about this. I think all it would make sense to have a common
> >>>> prefix for all reports coming form vfio-ccw (QEMU). But then I was like, that
> >>>> is a separate patch.
> >>>>
> >>>> Maybe something like:
> >>>> vfio-ccw (xx.xx.xxxx): specific message
> >>>>
> >>>> OTOH we don't seem to do that elsewhere (git grep -e 'warn\|error_report\|error_setg' -- hw/s390x/).
> >>>> AFAIR the error_setg captures context (like, src, line, func) but does not
> >>>> necessarily report it. Another question is if this should be extended to
> >>>> hw/s390x/s390-ccw.c
> >>>>
> >>>> What do you think?  
> >>> I'm not sure that makes sense, especially as not everything might
> >>> explicitly refer to a certain subchannel.
> >>>
> >>> Let's just add the subchannel id here? In this case, this is really a
> >>> useful piece of information (which device is showing this behaviour?)
> >>>      
> >>
> >> The same applies to  warn_report("vfio-ccw requires PFCH flag set") (that is,
> >> on which device (that has no force-orb-pfch=on specified)  is the guest issuing
> >> ORBs with the PFCH unset), or?
> >> Should I go for
> >> "vfio-ccw (xx.xx.xxxx): vfio-ccw requires PFCH flag set"
> >> and
> >> "vfio-ccw (xx.xx.xxxx): PFCH flag forced"
> >> or just for the second one, or some third option?  
> > 
> > Yes, it makes sense for both.
> > 
> > Related: Do we expect the guest driver to learn from its experience and
> > not try without pfch again? It is probably not very helpful if the logs
> > get filled with a lot of "vfio-ccw requires pfch" messages...
> >   
> 
> Don't really know. Dong Jia is probably more qualified to answer that question.
> I don't expect the guest driver to do so. There are probably more intelligent
> strategies to deal with this, but the question is what do we gain in the end
> (linux guests are not affected). We should probably not overthink this.

So, print both messages just once per device?