linux-kernel - Re: [PATCH] kvm_host: bump KVM_MAX_IRQ

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Date: Tue, 18 Jun 2024 14:28:46 +0200
From: Igor Mammedov <imammedo@...hat.com>
To: Daniil Tatianin <d-tatianin@...dex-team.ru>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
 linux-kernel@...r.kernel.org, yc-core@...dex-team.ru, Sean Christopherson
 <seanjc@...gle.com>
Subject: Re: [PATCH] kvm_host: bump KVM_MAX_IRQ_ROUTE to 128k

On Thu, 21 Mar 2024 11:24:42 +0300
Daniil Tatianin <d-tatianin@...dex-team.ru> 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@...dex-team.ru>

LGTM

Acked-by: Igor Mammedov <imammedo@...hat.com>

> ---
>  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,