From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from out30-131.freemail.mail.aliyun.com ([115.124.30.131]:38163 "EHLO out30-131.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726430AbgD2CU3 (ORCPT ); Tue, 28 Apr 2020 22:20:29 -0400 Subject: Re: [PATCH v2 1/7] KVM: s390: clean up redundant 'kvm_run' parameters References: <20200422125810.34847-1-tianjia.zhang@linux.alibaba.com> <20200422125810.34847-2-tianjia.zhang@linux.alibaba.com> <20200422154543.2efba3dd.cohuck@redhat.com> <20200422180403.03f60b0c.cohuck@redhat.com> <5e1e126d-f1b0-196c-594b-4289d0afb9a8@linux.alibaba.com> <20200423123901.72a4c6a4.cohuck@redhat.com> <71344f73-c34f-a373-49d1-5d839c6be5f6@linux.alibaba.com> <1d73b700-4a20-3d7a-66d1-29b5afa03f4d@de.ibm.com> <73f6ecd0-ac47-eaad-0e4f-2d41c2b34450@redhat.com> From: Tianjia Zhang Message-ID: <1b8167f2-eb91-5f17-8dc4-dcfaa5bbb075@linux.alibaba.com> Date: Wed, 29 Apr 2020 10:20:17 +0800 MIME-Version: 1.0 In-Reply-To: <73f6ecd0-ac47-eaad-0e4f-2d41c2b34450@redhat.com> Content-Type: text/plain; charset="utf-8"; format="flowed" Content-Transfer-Encoding: 8bit Sender: linux-s390-owner@vger.kernel.org List-ID: To: Thomas Huth , Christian Borntraeger , Cornelia Huck Cc: pbonzini@redhat.com, tsbogend@alpha.franken.de, paulus@ozlabs.org, mpe@ellerman.id.au, benh@kernel.crashing.org, frankja@linux.ibm.com, david@redhat.com, heiko.carstens@de.ibm.com, gor@linux.ibm.com, sean.j.christopherson@intel.com, vkuznets@redhat.com, wanpengli@tencent.com, jmattson@google.com, joro@8bytes.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, maz@kernel.org, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, christoffer.dall@arm.com, peterx@redhat.com, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-mips@vger.kernel.org, kvm-ppc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org 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 wrote: >>>> >>>>> On 2020/4/23 0:04, Cornelia Huck wrote: >>>>>> On Wed, 22 Apr 2020 17:58:04 +0200 >>>>>> Christian Borntraeger wrote: >>>>>> >>>>>>> On 22.04.20 15:45, Cornelia Huck wrote: >>>>>>>> On Wed, 22 Apr 2020 20:58:04 +0800 >>>>>>>> Tianjia Zhang 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 >>>>>>>>> --- >>>>>>>>>    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