Re: [v2 0/4] KVM: irqchip: synchronize srcu only if needed

[Christian Borntraeger]

Am 21.01.24 um 12:17 schrieb Yi Wang:
> From: Yi Wang <foxywang@xxxxxxxxxxx>
>
> We found that it may cost more than 20 milliseconds very accidentally
> to enable cap of KVM_CAP_SPLIT_IRQCHIP on a host which has many vms
> already.
>
> The reason is that when vmm(qemu/CloudHypervisor) invokes
> KVM_CAP_SPLIT_IRQCHIP kvm will call synchronize_srcu_expedited() and
> might_sleep and kworker of srcu may cost some delay during this period.
> One way makes sence is setup empty irq routing when creating vm and
> so that x86/s390 don't need to setup empty/dummy irq routing.
>
> Note: I have no s390 machine so the s390 patch has not been tested.

I just did a quick sniff and it still seems to work. No performance check etc.