linux-kernel - Re: [PATCH v2 1/7] KVM: s390: clean up redundant 'kvm

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Message-Id: <1d73b700-4a20-3d7a-66d1-29b5afa03f4d@de.ibm.com>
Date:   Thu, 23 Apr 2020 13:00:25 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>,
        Cornelia Huck <cohuck@...hat.com>
Cc:     pbonzini@...hat.com, tsbogend@...ha.franken.de, paulus@...abs.org,
        mpe@...erman.id.au, benh@...nel.crashing.org,
        frankja@...ux.ibm.com, david@...hat.com, heiko.carstens@...ibm.com,
        gor@...ux.ibm.com, sean.j.christopherson@...el.com,
        vkuznets@...hat.com, wanpengli@...cent.com, jmattson@...gle.com,
        joro@...tes.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, x86@...nel.org, hpa@...or.com, maz@...nel.org,
        james.morse@....com, julien.thierry.kdev@...il.com,
        suzuki.poulose@....com, christoffer.dall@....com,
        peterx@...hat.com, thuth@...hat.com, kvm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-mips@...r.kernel.org, kvm-ppc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/7] KVM: s390: clean up redundant 'kvm_run' parameters



On 23.04.20 12:58, Tianjia Zhang wrote:
> 
> 
> On 2020/4/23 18:39, Cornelia Huck wrote:
>> On Thu, 23 Apr 2020 11:01:43 +0800
>> Tianjia Zhang <tianjia.zhang@...ux.alibaba.com> wrote:
>>
>>> On 2020/4/23 0:04, Cornelia Huck wrote:
>>>> On Wed, 22 Apr 2020 17:58:04 +0200
>>>> Christian Borntraeger <borntraeger@...ibm.com> wrote:
>>>>   
>>>>> On 22.04.20 15:45, Cornelia Huck wrote:
>>>>>> On Wed, 22 Apr 2020 20:58:04 +0800
>>>>>> Tianjia Zhang <tianjia.zhang@...ux.alibaba.com> wrote:
>>>>>>      
>>>>>>> In the current kvm version, 'kvm_run' has been included in the 'kvm_vcpu'
>>>>>>> structure. Earlier than historical reasons, many kvm-related function
>>>>>>
>>>>>> s/Earlier than/For/ ?
>>>>>>      
>>>>>>> parameters retain the 'kvm_run' and 'kvm_vcpu' parameters at the same time.
>>>>>>> This patch does a unified cleanup of these remaining redundant parameters.
>>>>>>>
>>>>>>> Signed-off-by: Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
>>>>>>> ---
>>>>>>>    arch/s390/kvm/kvm-s390.c | 37 ++++++++++++++++++++++---------------
>>>>>>>    1 file changed, 22 insertions(+), 15 deletions(-)
>>>>>>>
>>>>>>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>>>>>>> index e335a7e5ead7..d7bb2e7a07ff 100644
>>>>>>> --- a/arch/s390/kvm/kvm-s390.c
>>>>>>> +++ b/arch/s390/kvm/kvm-s390.c
>>>>>>> @@ -4176,8 +4176,9 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
>>>>>>>        return rc;
>>>>>>>    }
>>>>>>>    -static void sync_regs_fmt2(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
>>>>>>> +static void sync_regs_fmt2(struct kvm_vcpu *vcpu)
>>>>>>>    {
>>>>>>> +    struct kvm_run *kvm_run = vcpu->run;
>>>>>>>        struct runtime_instr_cb *riccb;
>>>>>>>        struct gs_cb *gscb;
>>>>>>>    @@ -4235,7 +4236,7 @@ static void sync_regs_fmt2(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
>>>>>>>            }
>>>>>>>            if (vcpu->arch.gs_enabled) {
>>>>>>>                current->thread.gs_cb = (struct gs_cb *)
>>>>>>> -                        &vcpu->run->s.regs.gscb;
>>>>>>> +                        &kvm_run->s.regs.gscb;
>>>>>>
>>>>>> Not sure if these changes (vcpu->run-> => kvm_run->) are really worth
>>>>>> it. (It seems they amount to at least as much as the changes advertised
>>>>>> in the patch description.)
>>>>>>
>>>>>> Other opinions?
>>>>>
>>>>> Agreed. It feels kind of random. Maybe just do the first line (move kvm_run from the
>>>>> function parameter list into the variable declaration)? Not sure if this is better.
>>>>>   
>>>>
>>>> There's more in this patch that I cut... but I think just moving
>>>> kvm_run from the parameter list would be much less disruptive.
>>>>    
>>>
>>> I think there are two kinds of code(`vcpu->run->` and `kvm_run->`), but
>>> there will be more disruptive, not less.
>>
>> I just fail to see the benefit; sure, kvm_run-> is convenient, but the
>> current code is just fine, and any rework should be balanced against
>> the cost (e.g. cluttering git annotate).
>>
> 
> cluttering git annotate ? Does it mean Fix xxxx ("comment"). Is it possible to solve this problem by splitting this patch?

No its about breaking git blame (and bugfix backports) for just a cosmetic improvement.
And I agree with Conny: the cost is higher than the benefit.