linux-kernel - Re: [PATCH v2] KVM: Extend MAX_IRQ

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Date:   Fri, 20 Apr 2018 21:51:13 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Cornelia Huck <cohuck@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Tonny Lu <tonnylu@...cent.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>
Subject: Re: [PATCH v2] KVM: Extend MAX_IRQ_ROUTES to 4096 for all archs

2018-04-20 15:15 GMT+08:00 Cornelia Huck <cohuck@...hat.com>:
> On Thu, 19 Apr 2018 17:47:28 -0700
> Wanpeng Li <kernellwp@...il.com> wrote:
>
>> From: Wanpeng Li <wanpengli@...cent.com>
>>
>> Our virtual machines make use of device assignment by configuring
>> 12 NVMe disks for high I/O performance. Each NVMe device has 129
>> MSI-X Table entries:
>> Capabilities: [50] MSI-X: Enable+ Count=129 Masked-Vector table: BAR=0 offset=00002000
>> The windows virtual machines fail to boot since they will map the number of
>> MSI-table entries that the NVMe hardware reported to the bus to msi routing
>> table, this will exceed the 1024. This patch extends MAX_IRQ_ROUTES to 4096
>> for all archs, in the future this might be extended again if needed.
>>
>> Cc: Paolo Bonzini <pbonzini@...hat.com>
>> Cc: Radim Krčmář <rkrcmar@...hat.com>
>> Cc: Tonny Lu <tonnylu@...cent.com>
>> Cc: Cornelia Huck <cohuck@...hat.com>
>> Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
>> Signed-off-by: Tonny Lu <tonnylu@...cent.com>
>> ---
>> v1 -> v2:
>>  * extend MAX_IRQ_ROUTES to 4096 for all archs
>>
>>  include/linux/kvm_host.h | 6 ------
>>  1 file changed, 6 deletions(-)
>>
>> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
>> index 6930c63..0a5c299 100644
>> --- a/include/linux/kvm_host.h
>> +++ b/include/linux/kvm_host.h
>> @@ -1045,13 +1045,7 @@ static inline int mmu_notifier_retry(struct kvm *kvm, unsigned long mmu_seq)
>>
>>  #ifdef CONFIG_HAVE_KVM_IRQ_ROUTING
>>
>> -#ifdef CONFIG_S390
>>  #define KVM_MAX_IRQ_ROUTES 4096 //FIXME: we can have more than that...
>
> What about /* might need extension/rework in the future */ instead of
> the FIXME?

Yeah, I guess the maintainers can help to fix it when applying. :)

>
> As far as I understand, 4096 should cover most architectures and the
> sane end of s390 configurations, but will not be enough at the scarier
> end of s390. (I'm not sure how much it matters in practice.)
>
> Do we want to make this a tuneable in the future? Do some kind of
> dynamic allocation? Not sure whether it is worth the trouble.

I think keep as it is currently.

Regards,
Wanpeng Li