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.