Re: [PATCH] kvm_host: bump KVM_MAX_IRQ_ROUTE to 128k

[Daniil Tatianin]

On 6/18/24 3:28 PM, Igor Mammedov wrote:

> On Thu, 21 Mar 2024 11:24:42 +0300
> Daniil Tatianin <d-tatianin@xxxxxxxxxxxxxx> wrote:
>
> > We would like to be able to create large VMs (up to 224 vCPUs atm) with
> > up to 128 virtio-net cards, where each card needs a TX+RX queue per vCPU
> > for optimal performance (as well as config & control interrupts per
> > card). Adding in extra virtio-blk controllers with a queue per vCPU (up
> > to 192 disks) yields a total of about ~100k IRQ routes, rounded up to
> > 128k for extra headroom and flexibility.
> >
> > The current limit of 4096 was set in 2018 and is too low for modern
> > demands. It also seems to be there for no good reason as routes are
> > allocated lazily by the kernel anyway (depending on the largest GSI
> > requested by the VM).
> >
> > Signed-off-by: Daniil Tatianin <d-tatianin@xxxxxxxxxxxxxx>
> LGTM
>
> Acked-by: Igor Mammedov <imammedo@xxxxxxxxxx>

Thank you!

I want to ping everyone once again to take a look at this, I think this 
patch is quite trivial and unlocks larger VMs for free, would really 
appreciate a review from anyone interested!

> > ---
> >   include/linux/kvm_host.h | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index 48f31dcd318a..10a141add2a8 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -2093,7 +2093,7 @@ static inline bool mmu_invalidate_retry_gfn_unsafe(struct kvm *kvm,
> >   
> >   #ifdef CONFIG_HAVE_KVM_IRQ_ROUTING
> >   
> > -#define KVM_MAX_IRQ_ROUTES 4096 /* might need extension/rework in the future */
> > +#define KVM_MAX_IRQ_ROUTES 131072 /* might need extension/rework in the future */
> >   
> >   bool kvm_arch_can_set_irq_routing(struct kvm *kvm);
> >   int kvm_set_irq_routing(struct kvm *kvm,