From: James Morse <james.morse@arm.com> To: Zenghui Yu <yuzenghui@huawei.com> Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, christoffer.dall@arm.com, marc.zyngier@arm.com, acme@redhat.com, peterz@infradead.org, mingo@redhat.com, ganapatrao.kulkarni@cavium.com, catalin.marinas@arm.com, will.deacon@arm.com, mark.rutland@arm.com, acme@kernel.org, alexander.shishkin@linux.intel.com, jolsa@redhat.com, namhyung@kernel.org, wanghaibin.wang@huawei.com, xiexiangyou@huawei.com, linuxarm@huawei.com Subject: Re: [PATCH v1 2/5] KVM: arm/arm64: Adjust entry/exit and trap related tracepoints Date: Wed, 12 Jun 2019 13:49:14 +0100 Message-ID: <977f8f8c-72b4-0287-4b1c-47a0d6f1fd6e@arm.com> (raw) In-Reply-To: <1560330526-15468-3-git-send-email-yuzenghui@huawei.com> Hi, On 12/06/2019 10:08, Zenghui Yu wrote: > Currently, we use trace_kvm_exit() to report exception type (e.g., > "IRQ", "TRAP") and exception class (ESR_ELx's bit[31:26]) together. (They both caused an exit!) > But hardware only saves the exit class to ESR_ELx on synchronous EC is the 'Exception Class'. Exit is KVM/Linux's terminology. > exceptions, not on asynchronous exceptions. When the guest exits > due to external interrupts, we will get tracing output like: > > "kvm_exit: IRQ: HSR_EC: 0x0000 (UNKNOWN), PC: 0xffff87259e30" > > Obviously, "HSR_EC" here is meaningless. I assume we do it this way so there is only one guest-exit tracepoint that catches all exits. I don't think its a problem if user-space has to know the EC isn't set for asynchronous exceptions, this is a property of the architecture and anything using these trace-points is already arch specific. > This patch splits "exit" and "trap" events by adding two tracepoints > explicitly in handle_trap_exceptions(). Let trace_kvm_exit() report VM > exit events, and trace_kvm_trap_exit() report VM trap events. > > These tracepoints are adjusted also in preparation for supporting > 'perf kvm stat' on arm64. Because the existing tracepoints are ABI, I don't think we can change them. We can add new ones if there is something that a user reasonably needs to trace, and can't be done any other way. What can't 'perf kvm stat' do with the existing trace points? > diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c > index 516aead..af3c732 100644 > --- a/arch/arm64/kvm/handle_exit.c > +++ b/arch/arm64/kvm/handle_exit.c > @@ -264,7 +264,10 @@ static int handle_trap_exceptions(struct kvm_vcpu *vcpu, struct kvm_run *run) > exit_handle_fn exit_handler; > > exit_handler = kvm_get_exit_handler(vcpu); > + trace_kvm_trap_enter(vcpu->vcpu_id, > + kvm_vcpu_trap_get_class(vcpu)); > handled = exit_handler(vcpu, run); > + trace_kvm_trap_exit(vcpu->vcpu_id); > } Why are there two? Are you using this to benchmark the exit_handler()? As we can't remove the EC from the exit event, I don't think this tells us anything new. > diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c > index 90cedeb..9f63fd9 100644 > --- a/virt/kvm/arm/arm.c > +++ b/virt/kvm/arm/arm.c > @@ -758,7 +758,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run) > /************************************************************** > * Enter the guest > */ > - trace_kvm_entry(*vcpu_pc(vcpu)); > + trace_kvm_entry(vcpu->vcpu_id, *vcpu_pc(vcpu)); Why do you need the PC? It was exported on exit. (its mostly junk for user-space anyway, you can't infer anything from it) Thanks, James
next prev parent reply index Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-06-12 9:08 [PATCH v1 0/5] perf kvm: Add stat support on arm64 Zenghui Yu 2019-06-12 9:08 ` [PATCH v1 1/5] KVM: arm/arm64: Remove kvm_mmio_emulate tracepoint Zenghui Yu 2019-06-12 12:48 ` James Morse 2019-06-13 11:20 ` Zenghui Yu 2019-06-12 9:08 ` [PATCH v1 2/5] KVM: arm/arm64: Adjust entry/exit and trap related tracepoints Zenghui Yu 2019-06-12 12:49 ` James Morse [this message] 2019-06-13 11:28 ` Zenghui Yu 2019-06-17 11:19 ` James Morse 2019-06-21 13:25 ` Zenghui Yu 2019-06-12 9:08 ` [PATCH v1 3/5] perf tools arm64: Add support for get_cpuid() function Zenghui Yu 2019-06-12 9:08 ` [PATCH v1 4/5] perf,kvm/arm64: Add stat support on arm64 Zenghui Yu 2019-06-12 9:08 ` [PATCH v1 5/5] perf,kvm/arm64: perf-kvm-stat to report VM TRAP Zenghui Yu
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