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

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Message-ID: <ea0d1256-1236-4102-80fd-e0c05503c2fd@yandex-team.ru>
Date: Wed, 24 Jul 2024 13:23:47 +0300
From: Daniil Tatianin <d-tatianin@...dex-team.ru>
To: Igor Mammedov <imammedo@...hat.com>
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 6/18/24 3:28 PM, Igor Mammedov wrote:

> 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>

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,