Re: [PATCH v1] kvm: x86: implement PV send_IPI method

[Chao Gao]

On Fri, Jul 18, 2025 at 03:52:30PM +0800, Jason Wang wrote:
>On Fri, Jul 18, 2025 at 2:25 PM Cindy Lu <lulu@xxxxxxxxxx> wrote:
>>
>> From: Jason Wang <jasowang@xxxxxxxxxx>
>>
>> We used to have PV version of send_IPI_mask and
>> send_IPI_mask_allbutself. This patch implements PV send_IPI method to
>> reduce the number of vmexits.

It won't reduce the number of VM-exits; in fact, it may increase them on CPUs
that support IPI virtualization.

With IPI virtualization enabled, *unicast* and physical-addressing IPIs won't
cause a VM-exit. Instead, the microcode posts interrupts directly to the target
vCPU. The PV version always causes a VM-exit.

>>
>> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
>> Tested-by: Cindy Lu <lulu@xxxxxxxxxx>
>
>I think a question here is are we able to see performance improvement
>in any kind of setup?

It may result in a negative performance impact.

>
>Thanks
>
>