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Re: [Qemu-block] [Qemu-devel] [PATCH v2 1/1] virtio-scsi-ccw: use ioeven


From: Christian Borntraeger
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH v2 1/1] virtio-scsi-ccw: use ioeventfd even when KVM is disabled
Date: Tue, 4 Jul 2017 09:06:59 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.0

On 07/04/2017 05:41 AM, QingFeng Hao wrote:
> 
> 
> 在 2017/7/3 18:20, Christian Borntraeger 写道:
>> On 07/03/2017 10:51 AM, QingFeng Hao wrote:
>>> This patch is based on a similar patch from Stefan Hajnoczi -
>>> commit c324fd0a39c (" virtio-pci: use ioeventfd even when KVM is disabled)
>>>
>>> Do not check kvm_eventfds_enabled() when KVM is disabled since it
>>> always returns 0.  Since commit 8c56c1a592b5092d91da8d8943c17777d6462a6f
>>> ("memory: emulate ioeventfd") it has been possible to use ioeventfds in
>>> qtest or TCG mode.
>>>
>>> This patch makes -device virtio-scsi-ccw,iothread=iothread0 work even
>>> when KVM is disabled.
>>>
>>> I have tested that virtio-scsi-ccw works under tcg both with and without
>>> iothread.
>>>
>>> This patch fixes qemu-iotests 068, which was accidentally merged early
>>> despite the dependency on ioeventfd.
>>>
>>> Signed-off-by: QingFeng Hao <address@hidden>
>>> ---
>>>   hw/s390x/virtio-ccw.c | 2 +-
>>>   target/s390x/kvm.c    | 3 +++
>>>   2 files changed, 4 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/hw/s390x/virtio-ccw.c b/hw/s390x/virtio-ccw.c
>>> index 90d37cb9ff..35896eb007 100644
>>> --- a/hw/s390x/virtio-ccw.c
>>> +++ b/hw/s390x/virtio-ccw.c
>>> @@ -711,7 +711,7 @@ static void virtio_ccw_device_realize(VirtioCcwDevice 
>>> *dev, Error **errp)
>>>           sch->cssid, sch->ssid, sch->schid, sch->devno,
>>>           ccw_dev->devno.valid ? "user-configured" : "auto-configured");
>>>
>>> -    if (!kvm_eventfds_enabled()) {
>>> +    if (kvm_enabled() && !kvm_eventfds_enabled()) {
>>>           dev->flags &= ~VIRTIO_CCW_FLAG_USE_IOEVENTFD;
>>>       }
>>>
>>> diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
>>> index a3d00196f4..c37f9c3b9e 100644
>>> --- a/target/s390x/kvm.c
>>> +++ b/target/s390x/kvm.c
>>> @@ -2220,6 +2220,9 @@ int kvm_s390_assign_subch_ioeventfd(EventNotifier 
>>> *notifier, uint32_t sch,
>>>           .addr = sch,
>>>           .len = 8,
>>>       };
>>> +    if (!kvm_enabled()) {
>>> +        return 0;
>>> +    }
>> thinking more about it. wouldnt it be better to do something like this 
>> instead
>>
>> diff --git a/target/s390x/cpu.h b/target/s390x/cpu.h
>> index 058ddad..cc47831 100644
>> --- a/target/s390x/cpu.h
>> +++ b/target/s390x/cpu.h
>> @@ -1240,7 +1240,11 @@ static inline int 
>> s390_assign_subch_ioeventfd(EventNotifier *notifier,
>>                                                 uint32_t sch_id, int vq,
>>                                                 bool assign)
>>   {
>> -    return kvm_s390_assign_subch_ioeventfd(notifier, sch_id, vq, assign);
>> +    if (kvm_enabled()) {
>> +        return kvm_s390_assign_subch_ioeventfd(notifier, sch_id, vq, 
>> assign);
>> +    } else {
>> +        return 0;
>> +    }
>>   }
> Thanks. It makes sense. I'll change it.
>>   static inline void s390_crypto_reset(void)
>>
>>
>> FWIW, it seems that we (s390) do not have a functional equivalent function 
>> as commit
>> 8c56c1a592b5092d91da8d8943c17777d6462a6f ("memory: emulate ioeventfd") , so 
>> we will
>> not use the iothreads.
> Ok, but might s390 have skipped the iothread arguments and passed the test, 
> so we could
> still keep this test case?

Yes, lets just fix the test case. We can implement emulated ioeventfds later.




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