Re: [Qemu-devel] [PATCH v1 2/4] s390x/zpci: use hotplug_dev instead of looking up the host bridge

[David Hildenbrand]

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 <address@hidden> wrote:
>>>
>>>> We directly have it in our hands.
>>>>
>>>> Signed-off-by: David Hildenbrand <address@hidden>
>>>> ---
>>>>  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.

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.


-- 

Thanks,

David / dhildenb