From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:53653) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gKiAH-0004OC-Ql for qemu-devel@nongnu.org; Thu, 08 Nov 2018 06:08:00 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gKiAC-0001l4-TP for qemu-devel@nongnu.org; Thu, 08 Nov 2018 06:07:57 -0500 Date: Thu, 8 Nov 2018 12:07:41 +0100 From: Cornelia Huck Message-ID: <20181108120741.2e463fe2.cohuck@redhat.com> In-Reply-To: References: <20181105110313.29312-1-david@redhat.com> <20181105110313.29312-3-david@redhat.com> <20181105122148.2eae5288.cohuck@redhat.com> <3ba91b23-fbea-edce-3f2e-d3405cb3b4f7@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v1 2/4] s390x/zpci: use hotplug_dev instead of looking up the host bridge List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Collin Walling Cc: David Hildenbrand , Christian Borntraeger , "Michael S . Tsirkin" , Alexander Graf , qemu-devel@nongnu.org, qemu-s390x@nongnu.org, Thomas Huth , Igor Mammedov , Richard Henderson On Wed, 7 Nov 2018 15:28:31 -0500 Collin Walling 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 wrote: > >>>> > >>>>> We directly have it in our hands. > >>>>> > >>>>> Signed-off-by: David Hildenbrand > >>>>> --- > >>>>> 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.