linux-kernel - Re: [PATCH v5 05/15] KVM: s390: unify pending_irqs() and pending_irqs_no

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Date:   Thu, 20 Dec 2018 17:40:46 +0100
From:   Michael Mueller <mimu@...ux.ibm.com>
To:     pierre morel <pmorel@...s.fr>, Cornelia Huck <cohuck@...hat.com>
Cc:     KVM Mailing List <kvm@...r.kernel.org>,
        Linux-S390 Mailing List <linux-s390@...r.kernel.org>,
        linux-kernel@...r.kernel.org,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Halil Pasic <pasic@...ux.ibm.com>,
        Pierre Morel <pmorel@...ux.ibm.com>
Subject: Re: [PATCH v5 05/15] KVM: s390: unify pending_irqs() and
 pending_irqs_no_gisa()



On 20.12.18 16:43, pierre morel wrote:
> 
> 
> Le 12/20/18 à 13:33, Michael Mueller a écrit :
>>
>>
>> On 20.12.18 13:21, Cornelia Huck wrote:
>>> On Thu, 20 Dec 2018 12:49:56 +0100
>>> Michael Mueller <mimu@...ux.ibm.com> wrote:
>>>
>>>> On 20.12.18 12:06, Cornelia Huck wrote:
>>>>> On Wed, 19 Dec 2018 20:17:46 +0100
>>>>> Michael Mueller <mimu@...ux.ibm.com> wrote:
>>>>>> Use a single function with parameter irq_flags to differentiate
>>>>>> between cases.
>>>>>>
> ...snip
>>>>>>    }
>>>>>> -static inline unsigned long pending_irqs_no_gisa(struct kvm_vcpu 
>>>>>> *vcpu)
>>>>>> +static inline unsigned long pending_irqs(struct kvm_vcpu *vcpu, 
>>>>>> u16 irq_flags)
>>>>>
>>>>> Any deeper reason why this is a u16? 16 bits should be enough for
>>>>> everyone? :)
>>>>
>>>> I want to use the 8 bits for the IRQ type and the other 8 for 
>>>> additional
>>>> controls, see: "KVM: s390: restore IAM in get_ipm() when IPM is clean"
>>>
>>> Still need to look at that patch, but my question mainly was "why only
>>> 16 bits"? I would think making this local variable larger is cheap.
>>>
> 
> +1
> 
>>
>> I will enlarge the flag mask to u32 with 16 bits for the IRQ types then.
> 
> AFAIK CPU generally work better with int (or long)
> Is there any hardware reason to restrict the size?

It's already changed to 4 bytes

> 
>>
>>>>
>>>>>>    {
>>>>>> -    return vcpu->kvm->arch.float_int.pending_irqs |
>>>>>> -        vcpu->arch.local_int.pending_irqs;
>>>>>> -}
>>>
>>
>