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Re: [qemu-s390x] [Qemu-devel] [PATCH v1 2/4] s390x/zpci: use hotplug_dev
From: |
Collin Walling |
Subject: |
Re: [qemu-s390x] [Qemu-devel] [PATCH v1 2/4] s390x/zpci: use hotplug_dev instead of looking up the host bridge |
Date: |
Wed, 7 Nov 2018 15:28:31 -0500 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 |
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 <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.
>
>
Truthfully, I'm not in favor of one over the other. As long as the device
handlers
are consistent, I think either is fine.
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.
--
Respectfully,
- Collin Walling
- [qemu-s390x] [PATCH v1 3/4] s390x/zpci: move some hotplug checks to the pre_plug handler, (continued)
[qemu-s390x] [PATCH v1 2/4] s390x/zpci: use hotplug_dev instead of looking up the host bridge, David Hildenbrand, 2018/11/05
- Re: [qemu-s390x] [PATCH v1 2/4] s390x/zpci: use hotplug_dev instead of looking up the host bridge, Cornelia Huck, 2018/11/05
- Re: [qemu-s390x] [PATCH v1 2/4] s390x/zpci: use hotplug_dev instead of looking up the host bridge, David Hildenbrand, 2018/11/05
- Re: [qemu-s390x] [PATCH v1 2/4] s390x/zpci: use hotplug_dev instead of looking up the host bridge, Christian Borntraeger, 2018/11/05
- Re: [qemu-s390x] [PATCH v1 2/4] s390x/zpci: use hotplug_dev instead of looking up the host bridge, David Hildenbrand, 2018/11/05
- Re: [qemu-s390x] [Qemu-devel] [PATCH v1 2/4] s390x/zpci: use hotplug_dev instead of looking up the host bridge,
Collin Walling <=
- Re: [qemu-s390x] [Qemu-devel] [PATCH v1 2/4] s390x/zpci: use hotplug_dev instead of looking up the host bridge, Cornelia Huck, 2018/11/08
- Re: [qemu-s390x] [Qemu-devel] [PATCH v1 2/4] s390x/zpci: use hotplug_dev instead of looking up the host bridge, David Hildenbrand, 2018/11/08
Re: [qemu-s390x] [PATCH v1 0/4] s390x/zpci: some hotplug handler cleanups, Cornelia Huck, 2018/11/12