Messages in this thread | | | Subject | Re: [PATCH v2 1/7] KVM: s390: clean up redundant 'kvm_run' parameters | From | Tianjia Zhang <> | Date | Wed, 29 Apr 2020 10:20:17 +0800 |
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On 2020/4/26 20:59, Thomas Huth wrote: > On 23/04/2020 13.00, Christian Borntraeger wrote: >> >> >> 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@linux.alibaba.com> wrote: >>>> >>>>> On 2020/4/23 0:04, Cornelia Huck wrote: >>>>>> On Wed, 22 Apr 2020 17:58:04 +0200 >>>>>> Christian Borntraeger <borntraeger@de.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@linux.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@linux.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. > > It could be slightly more than a cosmetic improvement (depending on the > smartness of the compiler): vcpu->run-> are two dereferences, while > kvm_run-> is only one dereference. So it could be slightly more compact > and faster code. > > Thomas >
If the compiler is smart enough, this place can be automatically optimized, but we can't just rely on the compiler, if not? This requires a trade-off between code cleanliness readability and breaking git blame. In addition, I have removed the changes here and sent a v4 patch. Please also help review it.
Thanks and best, Tianjia
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