On Wed, 7 Nov 2018 15:28:31 -0500
Collin Walling <wall...@linux.ibm.com> wrote:
> On 11/5/18 6:50 AM, David Hildenbrand wrote:
> > On 05.11.18 12:40, Christian Borntraeger wrote:
> >>
> >>
> >> On 11/05/2018 12:37 PM, David Hildenbrand wrote:
> >>> On 05.11.18 12:21, Cornelia Huck wrote:
> >>>> On Mon, 5 Nov 2018 12:03:11 +0100
> >>>> David Hildenbrand <da...@redhat.com> wrote:
> >>>>
> >>>>> We directly have it in our hands.
> >>>>>
> >>>>> Signed-off-by: David Hildenbrand <da...@redhat.com>
> >>>>> ---
> >>>>> hw/s390x/s390-pci-bus.c | 4 ++--
> >>>>> 1 file changed, 2 insertions(+), 2 deletions(-)
> >>>>>
> >>>>> diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c
> >>>>> index 1eaae3aca6..68660eac74 100644
> >>>>> --- a/hw/s390x/s390-pci-bus.c
> >>>>> +++ b/hw/s390x/s390-pci-bus.c
> >>>>> @@ -814,9 +814,9 @@ static bool s390_pci_alloc_idx(S390pciState *s,
> >>>>> S390PCIBusDevice *pbdev)
> >>>>> static void s390_pcihost_plug(HotplugHandler *hotplug_dev, DeviceState
> >>>>> *dev,
> >>>>> Error **errp)
> >>>>> {
> >>>>> + S390pciState *s = S390_PCI_HOST_BRIDGE(hotplug_dev);
> >>>>> PCIDevice *pdev = NULL;
> >>>>> S390PCIBusDevice *pbdev = NULL;
> >>>>> - S390pciState *s = s390_get_phb();
> >>>>>
> >>>>> if (object_dynamic_cast(OBJECT(dev), TYPE_PCI_BRIDGE)) {
> >>>>> BusState *bus;
> >>>>> @@ -924,11 +924,11 @@ static void s390_pcihost_timer_cb(void *opaque)
> >>>>> static void s390_pcihost_unplug(HotplugHandler *hotplug_dev,
> >>>>> DeviceState *dev,
> >>>>> Error **errp)
> >>>>> {
> >>>>> + S390pciState *s = S390_PCI_HOST_BRIDGE(hotplug_dev);
> >>>>> PCIDevice *pci_dev = NULL;
> >>>>> PCIBus *bus;
> >>>>> int32_t devfn;
> >>>>> S390PCIBusDevice *pbdev = NULL;
> >>>>> - S390pciState *s = s390_get_phb();
> >>>>>
> >>>>> if (object_dynamic_cast(OBJECT(dev), TYPE_PCI_BRIDGE)) {
> >>>>> error_setg(errp, "PCI bridge hot unplug currently not
> >>>>> supported");
> >>>>
> >>>> Not sure whether that is an improvement (s390_get_phb() caches the
> >>>> value, and is called from multiple other places as well.)
> >>>>
> >>>
> >>> Looking up a variable that is directly passed as an argument doesn't
> >>> look clean to me.
> >>
> >> I think there was a reason for this caching, namely that qom resolution can
> >> be quite expensive. For the hotplug case this obviously does not matter but
> >> for all the other cases it might. So do we really want to have different
> >> places use different methods?
> >>
> >
> > Caching resolution is fine (as that is expensive), caching a downcast is
> > as far as I remember not necessary. Especially, as you said, for hotplug
> > handlers.
Yes, the complete QOM cast was the expensive thing AFAIR.
> >
> > Anyhow, if there are strong feelings to this change, I can drop this
> > patch. There are certainly more important things to do in zPCI hotplug code.
> >
> >
>
> Truthfully, I'm not in favor of one over the other. As long as the device
> handlers
> are consistent, I think either is fine.
I don't feel *that* strong about this change here, either :) Your call.
>
> However, it would be nice if at some point during plug we cache the PHB
> somewhere.
> That would be some sort of best-of-both-worlds approach.
Not sure if caching-from-a-downcast would be conceptionally clean. I'd
vote for either taking this patch or dropping it completely.
