* Re: [PATCH v2] s390x/pci: set kvm_msi_via_irqfd_allowed
2025-10-07 20:56 [PATCH v2] s390x/pci: set kvm_msi_via_irqfd_allowed Matthew Rosato
@ 2025-10-07 22:14 ` Farhan Ali
2025-10-08 8:49 ` David Hildenbrand
` (2 subsequent siblings)
3 siblings, 0 replies; 7+ messages in thread
From: Farhan Ali @ 2025-10-07 22:14 UTC (permalink / raw)
To: Matthew Rosato, qemu-s390x
Cc: farman, thuth, pasic, borntraeger, richard.henderson, david, iii,
qemu-devel
Reviewed-by: Farhan Ali <alifm@linux.ibm.com>
On 10/7/2025 1:56 PM, Matthew Rosato wrote:
> Allow irqfd to be used for virtio-pci on s390x if the kernel supports
> it. This improves s390x virtio-pci performance when using kvm
> acceleration by allowing kvm to deliver interrupts instead of QEMU.
>
> Reviewed-by: Eric Farman <farman@linux.ibm.com>
> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
> ---
> v2:
> - add review tag
> - tweak commit message (David)
> ---
> hw/s390x/s390-pci-bus.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c
> index e8e41c8a9a..88852acf45 100644
> --- a/hw/s390x/s390-pci-bus.c
> +++ b/hw/s390x/s390-pci-bus.c
> @@ -900,6 +900,7 @@ static void s390_pcihost_realize(DeviceState *dev, Error **errp)
> s390_pci_init_default_group();
> css_register_io_adapters(CSS_IO_ADAPTER_PCI, true, false,
> S390_ADAPTER_SUPPRESSIBLE, errp);
> + kvm_msi_via_irqfd_allowed = kvm_irqfds_enabled();
> }
>
> static void s390_pcihost_unrealize(DeviceState *dev)
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH v2] s390x/pci: set kvm_msi_via_irqfd_allowed
2025-10-07 20:56 [PATCH v2] s390x/pci: set kvm_msi_via_irqfd_allowed Matthew Rosato
2025-10-07 22:14 ` Farhan Ali
@ 2025-10-08 8:49 ` David Hildenbrand
2025-10-08 10:23 ` Halil Pasic
2025-10-08 12:51 ` Thomas Huth
3 siblings, 0 replies; 7+ messages in thread
From: David Hildenbrand @ 2025-10-08 8:49 UTC (permalink / raw)
To: Matthew Rosato, qemu-s390x
Cc: farman, thuth, pasic, borntraeger, richard.henderson, iii,
qemu-devel
On 07.10.25 22:56, Matthew Rosato wrote:
> Allow irqfd to be used for virtio-pci on s390x if the kernel supports
> it. This improves s390x virtio-pci performance when using kvm
> acceleration by allowing kvm to deliver interrupts instead of QEMU.
>
> Reviewed-by: Eric Farman <farman@linux.ibm.com>
> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
> ---
Reviewed-by: David Hildenbrand <david@redhat.com>
--
Cheers
David / dhildenb
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v2] s390x/pci: set kvm_msi_via_irqfd_allowed
2025-10-07 20:56 [PATCH v2] s390x/pci: set kvm_msi_via_irqfd_allowed Matthew Rosato
2025-10-07 22:14 ` Farhan Ali
2025-10-08 8:49 ` David Hildenbrand
@ 2025-10-08 10:23 ` Halil Pasic
2025-10-08 12:51 ` Thomas Huth
3 siblings, 0 replies; 7+ messages in thread
From: Halil Pasic @ 2025-10-08 10:23 UTC (permalink / raw)
To: Matthew Rosato
Cc: qemu-s390x, farman, thuth, borntraeger, richard.henderson, david,
iii, qemu-devel, Halil Pasic
On Tue, 7 Oct 2025 16:56:14 -0400
Matthew Rosato <mjrosato@linux.ibm.com> wrote:
> Allow irqfd to be used for virtio-pci on s390x if the kernel supports
> it. This improves s390x virtio-pci performance when using kvm
> acceleration by allowing kvm to deliver interrupts instead of QEMU.
>
> Reviewed-by: Eric Farman <farman@linux.ibm.com>
> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v2] s390x/pci: set kvm_msi_via_irqfd_allowed
2025-10-07 20:56 [PATCH v2] s390x/pci: set kvm_msi_via_irqfd_allowed Matthew Rosato
` (2 preceding siblings ...)
2025-10-08 10:23 ` Halil Pasic
@ 2025-10-08 12:51 ` Thomas Huth
2025-10-08 13:19 ` Matthew Rosato
3 siblings, 1 reply; 7+ messages in thread
From: Thomas Huth @ 2025-10-08 12:51 UTC (permalink / raw)
To: Matthew Rosato, qemu-s390x
Cc: farman, pasic, borntraeger, richard.henderson, david, iii,
qemu-devel
On 07/10/2025 22.56, Matthew Rosato wrote:
> Allow irqfd to be used for virtio-pci on s390x if the kernel supports
> it. This improves s390x virtio-pci performance when using kvm
> acceleration by allowing kvm to deliver interrupts instead of QEMU.
>
> Reviewed-by: Eric Farman <farman@linux.ibm.com>
> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
> ---
> v2:
> - add review tag
> - tweak commit message (David)
> ---
> hw/s390x/s390-pci-bus.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c
> index e8e41c8a9a..88852acf45 100644
> --- a/hw/s390x/s390-pci-bus.c
> +++ b/hw/s390x/s390-pci-bus.c
> @@ -900,6 +900,7 @@ static void s390_pcihost_realize(DeviceState *dev, Error **errp)
> s390_pci_init_default_group();
> css_register_io_adapters(CSS_IO_ADAPTER_PCI, true, false,
> S390_ADAPTER_SUPPRESSIBLE, errp);
> + kvm_msi_via_irqfd_allowed = kvm_irqfds_enabled();
> }
Hi Matthew,
this unfortunately fails to compile without KVM (e.g. on x86 hosts):
../../devel/qemu/hw/s390x/s390-pci-bus.c: In function ‘s390_pcihost_realize’:
../../devel/qemu/hw/s390x/s390-pci-bus.c:903:5: error:
‘kvm_msi_via_irqfd_allowed’ undeclared (first use in this function); did you
mean ‘kvm_msi_via_irqfd_enabled’?
903 | kvm_msi_via_irqfd_allowed = kvm_irqfds_enabled();
| ^~~~~~~~~~~~~~~~~~~~~~~~~
| kvm_msi_via_irqfd_enabled
../../devel/qemu/hw/s390x/s390-pci-bus.c:903:5: note: each undeclared
identifier is reported only once for each function it appears in
Thomas
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH v2] s390x/pci: set kvm_msi_via_irqfd_allowed
2025-10-08 12:51 ` Thomas Huth
@ 2025-10-08 13:19 ` Matthew Rosato
2025-10-08 13:44 ` Thomas Huth
0 siblings, 1 reply; 7+ messages in thread
From: Matthew Rosato @ 2025-10-08 13:19 UTC (permalink / raw)
To: Thomas Huth, qemu-s390x
Cc: farman, pasic, borntraeger, richard.henderson, david, iii,
qemu-devel
On 10/8/25 8:51 AM, Thomas Huth wrote:
> On 07/10/2025 22.56, Matthew Rosato wrote:
>> Allow irqfd to be used for virtio-pci on s390x if the kernel supports
>> it. This improves s390x virtio-pci performance when using kvm
>> acceleration by allowing kvm to deliver interrupts instead of QEMU.
>>
>> Reviewed-by: Eric Farman <farman@linux.ibm.com>
>> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
>> ---
>> v2:
>> - add review tag
>> - tweak commit message (David)
>> ---
>> hw/s390x/s390-pci-bus.c | 1 +
>> 1 file changed, 1 insertion(+)
>>
>> diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c
>> index e8e41c8a9a..88852acf45 100644
>> --- a/hw/s390x/s390-pci-bus.c
>> +++ b/hw/s390x/s390-pci-bus.c
>> @@ -900,6 +900,7 @@ static void s390_pcihost_realize(DeviceState *dev, Error **errp)
>> s390_pci_init_default_group();
>> css_register_io_adapters(CSS_IO_ADAPTER_PCI, true, false,
>> S390_ADAPTER_SUPPRESSIBLE, errp);
>> + kvm_msi_via_irqfd_allowed = kvm_irqfds_enabled();
>> }
>
> Hi Matthew,
>
> this unfortunately fails to compile without KVM (e.g. on x86 hosts):
>
> ../../devel/qemu/hw/s390x/s390-pci-bus.c: In function ‘s390_pcihost_realize’:
> ../../devel/qemu/hw/s390x/s390-pci-bus.c:903:5: error: ‘kvm_msi_via_irqfd_allowed’ undeclared (first use in this function); did you mean ‘kvm_msi_via_irqfd_enabled’?
> 903 | kvm_msi_via_irqfd_allowed = kvm_irqfds_enabled();
> | ^~~~~~~~~~~~~~~~~~~~~~~~~
> | kvm_msi_via_irqfd_enabled
> ../../devel/qemu/hw/s390x/s390-pci-bus.c:903:5: note: each undeclared identifier is reported only once for each function it appears in
>
Argh, thanks for pointing this out. Of course this value only exists when CONFIG_KVM...
What do you think about using a routine in hw/s390x/s390-pci-kvm.c to set the value (and is a NOP stub when !CONFIG_KVM)?
Thanks,
Matt
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v2] s390x/pci: set kvm_msi_via_irqfd_allowed
2025-10-08 13:19 ` Matthew Rosato
@ 2025-10-08 13:44 ` Thomas Huth
0 siblings, 0 replies; 7+ messages in thread
From: Thomas Huth @ 2025-10-08 13:44 UTC (permalink / raw)
To: Matthew Rosato, qemu-s390x
Cc: farman, pasic, borntraeger, richard.henderson, david, iii,
qemu-devel
On 08/10/2025 15.19, Matthew Rosato wrote:
> On 10/8/25 8:51 AM, Thomas Huth wrote:
>> On 07/10/2025 22.56, Matthew Rosato wrote:
>>> Allow irqfd to be used for virtio-pci on s390x if the kernel supports
>>> it. This improves s390x virtio-pci performance when using kvm
>>> acceleration by allowing kvm to deliver interrupts instead of QEMU.
>>>
>>> Reviewed-by: Eric Farman <farman@linux.ibm.com>
>>> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
>>> ---
>>> v2:
>>> - add review tag
>>> - tweak commit message (David)
>>> ---
>>> hw/s390x/s390-pci-bus.c | 1 +
>>> 1 file changed, 1 insertion(+)
>>>
>>> diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c
>>> index e8e41c8a9a..88852acf45 100644
>>> --- a/hw/s390x/s390-pci-bus.c
>>> +++ b/hw/s390x/s390-pci-bus.c
>>> @@ -900,6 +900,7 @@ static void s390_pcihost_realize(DeviceState *dev, Error **errp)
>>> s390_pci_init_default_group();
>>> css_register_io_adapters(CSS_IO_ADAPTER_PCI, true, false,
>>> S390_ADAPTER_SUPPRESSIBLE, errp);
>>> + kvm_msi_via_irqfd_allowed = kvm_irqfds_enabled();
>>> }
>>
>> Hi Matthew,
>>
>> this unfortunately fails to compile without KVM (e.g. on x86 hosts):
>>
>> ../../devel/qemu/hw/s390x/s390-pci-bus.c: In function ‘s390_pcihost_realize’:
>> ../../devel/qemu/hw/s390x/s390-pci-bus.c:903:5: error: ‘kvm_msi_via_irqfd_allowed’ undeclared (first use in this function); did you mean ‘kvm_msi_via_irqfd_enabled’?
>> 903 | kvm_msi_via_irqfd_allowed = kvm_irqfds_enabled();
>> | ^~~~~~~~~~~~~~~~~~~~~~~~~
>> | kvm_msi_via_irqfd_enabled
>> ../../devel/qemu/hw/s390x/s390-pci-bus.c:903:5: note: each undeclared identifier is reported only once for each function it appears in
>>
>
> Argh, thanks for pointing this out. Of course this value only exists when CONFIG_KVM...
>
> What do you think about using a routine in hw/s390x/s390-pci-kvm.c to set the value (and is a NOP stub when !CONFIG_KVM)?
Yes, since we're doing this for some other KVM-related functions there
already, that sounds like the right way to go here.
Thomas
^ permalink raw reply [flat|nested] 7+ messages in thread