From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:59526 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725974AbgDZM7o (ORCPT ); Sun, 26 Apr 2020 08:59:44 -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> From: Thomas Huth Message-ID: <73f6ecd0-ac47-eaad-0e4f-2d41c2b34450@redhat.com> Date: Sun, 26 Apr 2020 14:59:18 +0200 MIME-Version: 1.0 In-Reply-To: <1d73b700-4a20-3d7a-66d1-29b5afa03f4d@de.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable Sender: linux-s390-owner@vger.kernel.org List-ID: To: Christian Borntraeger , Tianjia Zhang , 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 23/04/2020 13.00, Christian Borntraeger wrote: >=20 >=20 > 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: >>>>> =C2=A0=C2=A0 >>>>>> On 22.04.20 15:45, Cornelia Huck wrote: >>>>>>> On Wed, 22 Apr 2020 20:58:04 +0800 >>>>>>> Tianjia Zhang wrote: >>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 >>>>>>>> In the current kvm version, 'kvm_run' has been included in the '= kvm_vcpu' >>>>>>>> structure. Earlier than historical reasons, many kvm-related fun= ction >>>>>>> >>>>>>> s/Earlier than/For/ ? >>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 >>>>>>>> parameters retain the 'kvm_run' and 'kvm_vcpu' parameters at the= same time. >>>>>>>> This patch does a unified cleanup of these remaining redundant p= arameters. >>>>>>>> >>>>>>>> Signed-off-by: Tianjia Zhang >>>>>>>> --- >>>>>>>> =C2=A0=C2=A0 arch/s390/kvm/kvm-s390.c | 37 +++++++++++++++++++++= +--------------- >>>>>>>> =C2=A0=C2=A0 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 *vcp= u) >>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return rc; >>>>>>>> =C2=A0=C2=A0 } >>>>>>>> =C2=A0=C2=A0 -static void sync_regs_fmt2(struct kvm_vcpu *vcpu, = struct kvm_run *kvm_run) >>>>>>>> +static void sync_regs_fmt2(struct kvm_vcpu *vcpu) >>>>>>>> =C2=A0=C2=A0 { >>>>>>>> +=C2=A0=C2=A0=C2=A0 struct kvm_run *kvm_run =3D vcpu->run; >>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 struct runtime_instr_cb *ri= ccb; >>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 struct gs_cb *gscb; >>>>>>>> =C2=A0=C2=A0 @@ -4235,7 +4236,7 @@ static void sync_regs_fmt2(st= ruct kvm_vcpu *vcpu, struct kvm_run *kvm_run) >>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if = (vcpu->arch.gs_enabled) { >>>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0 current->thread.gs_cb =3D (struct gs_cb *) >>>>>>>> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= &vcpu->run->s.regs.gscb; >>>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= &kvm_run->s.regs.gscb; >>>>>>> >>>>>>> Not sure if these changes (vcpu->run-> =3D> kvm_run->) are really= worth >>>>>>> it. (It seems they amount to at least as much as the changes adve= rtised >>>>>>> in the patch description.) >>>>>>> >>>>>>> Other opinions? >>>>>> >>>>>> Agreed. It feels kind of random. Maybe just do the first line (mov= e kvm_run from the >>>>>> function parameter list into the variable declaration)? Not sure i= f this is better. >>>>>> =C2=A0=20 >>>>> >>>>> 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. >>>>> =C2=A0=C2=A0=20 >>>> >>>> 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 th= e >>> 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 pos= sible to solve this problem by splitting this patch? >=20 > No its about breaking git blame (and bugfix backports) for just a cosme= tic 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