From: Peter Zijlstra <peterz@infradead.org>
To: Andi Kleen <ak@linux.intel.com>
Cc: Like Xu <like.xu@linux.intel.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Borislav Petkov <bp@alien8.de>,
Sean Christopherson <seanjc@google.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
weijiang.yang@intel.com, Kan Liang <kan.liang@linux.intel.com>,
wei.w.wang@intel.com, eranian@google.com,
liuxiangdong5@huawei.com, linux-kernel@vger.kernel.org,
x86@kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH v6 07/16] KVM: x86/pmu: Reprogram PEBS event to emulate guest PEBS counter
Date: Tue, 18 May 2021 10:47:09 +0200 [thread overview]
Message-ID: <YKN/DVNt847iEctd@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <ff5a419f-188f-d14c-72c8-4b760052734d@linux.intel.com>
On Mon, May 17, 2021 at 07:44:15AM -0700, Andi Kleen wrote:
>
> On 5/17/2021 1:39 AM, Peter Zijlstra wrote:
> > On Tue, May 11, 2021 at 10:42:05AM +0800, Like Xu wrote:
> > > + if (pebs) {
> > > + /*
> > > + * The non-zero precision level of guest event makes the ordinary
> > > + * guest event becomes a guest PEBS event and triggers the host
> > > + * PEBS PMI handler to determine whether the PEBS overflow PMI
> > > + * comes from the host counters or the guest.
> > > + *
> > > + * For most PEBS hardware events, the difference in the software
> > > + * precision levels of guest and host PEBS events will not affect
> > > + * the accuracy of the PEBS profiling result, because the "event IP"
> > > + * in the PEBS record is calibrated on the guest side.
> > > + */
> > > + attr.precise_ip = 1;
> > > + }
> > You've just destroyed precdist, no?
>
> precdist can mean multiple things:
>
> - Convert cycles to the precise INST_RETIRED event. That is not meaningful
> for virtualization because "cycles" doesn't exist, just the raw events.
>
> - For GLC+ and TNT+ it will force the event to a specific counter that is
> more precise. This would be indeed "destroyed", but right now the patch kit
> only supports Icelake which doesn't support that anyways.
>
> So I think the code is correct for now, but will need to be changed for
> later CPUs. Should perhaps fix the comment though to discuss this.
OK, can we then do a better comment that explains *why* this is correct
now and what needs help later?
Because IIUC the only reason it is correct now is because:
- we only support ICL
* and ICL has pebs_format>=2, so {1,2} are the same
* and ICL doesn't have precise_ip==3 support
- Other hardware (GLC+, TNT+) that could possibly care here
is unsupported atm. but needs changes.
None of which is actually mentioned in that comment it does have.
next prev parent reply other threads:[~2021-05-18 8:47 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-11 2:41 [PATCH v6 00/16] KVM: x86/pmu: Add *basic* support to enable guest PEBS via DS Like Xu
2021-05-11 2:41 ` [PATCH v6 01/16] perf/x86/intel: Add EPT-Friendly PEBS for Ice Lake Server Like Xu
2021-05-11 2:42 ` [PATCH v6 02/16] perf/x86/intel: Handle guest PEBS overflow PMI for KVM guest Like Xu
2021-05-17 8:16 ` Peter Zijlstra
2021-05-18 7:38 ` Xu, Like
2021-05-18 8:37 ` Peter Zijlstra
2021-05-11 2:42 ` [PATCH v6 03/16] perf/x86/core: Pass "struct kvm_pmu *" to determine the guest values Like Xu
2021-05-11 2:42 ` [PATCH v6 04/16] KVM: x86/pmu: Set MSR_IA32_MISC_ENABLE_EMON bit when vPMU is enabled Like Xu
2021-05-12 1:58 ` Venkatesh Srinivas
2021-05-12 5:00 ` Xu, Like
2021-05-12 15:18 ` Sean Christopherson
2021-05-13 2:50 ` Xu, Like
2021-05-17 18:43 ` Venkatesh Srinivas
2021-05-17 21:19 ` Sean Christopherson
2021-05-17 21:16 ` Sean Christopherson
2021-05-17 23:51 ` Sean Christopherson
2021-05-18 7:49 ` Xu, Like
2021-05-11 2:42 ` [PATCH v6 05/16] KVM: x86/pmu: Introduce the ctrl_mask value for fixed counter Like Xu
2021-05-17 8:18 ` Peter Zijlstra
2021-05-18 7:55 ` Xu, Like
2021-05-18 8:35 ` Peter Zijlstra
2021-05-11 2:42 ` [PATCH v6 06/16] KVM: x86/pmu: Add IA32_PEBS_ENABLE MSR emulation for extended PEBS Like Xu
2021-05-17 8:32 ` Peter Zijlstra
2021-05-18 8:44 ` Xu, Like
2021-05-18 13:42 ` Peter Zijlstra
2021-05-17 8:33 ` Peter Zijlstra
2021-05-18 8:13 ` Xu, Like
2021-05-11 2:42 ` [PATCH v6 07/16] KVM: x86/pmu: Reprogram PEBS event to emulate guest PEBS counter Like Xu
2021-05-17 8:39 ` Peter Zijlstra
2021-05-17 14:44 ` Andi Kleen
2021-05-18 8:47 ` Peter Zijlstra [this message]
2021-05-18 13:15 ` Xu, Like
2021-05-18 15:58 ` Andi Kleen
2021-05-17 9:14 ` Peter Zijlstra
2021-05-18 13:28 ` Xu, Like
2021-05-18 13:36 ` Peter Zijlstra
2021-05-18 14:05 ` Xu, Like
2021-05-11 2:42 ` [PATCH v6 08/16] KVM: x86/pmu: Add IA32_DS_AREA MSR emulation to support guest DS Like Xu
2021-05-12 5:16 ` Xu, Like
2021-05-17 13:26 ` Peter Zijlstra
2021-05-17 14:50 ` Andi Kleen
2021-05-11 2:42 ` [PATCH v6 09/16] KVM: x86/pmu: Add PEBS_DATA_CFG MSR emulation to support adaptive PEBS Like Xu
2021-05-11 2:42 ` [PATCH v6 10/16] KVM: x86: Set PEBS_UNAVAIL in IA32_MISC_ENABLE when PEBS is enabled Like Xu
2021-05-11 2:42 ` [PATCH v6 11/16] KVM: x86/pmu: Adjust precise_ip to emulate Ice Lake guest PDIR counter Like Xu
2021-05-11 2:42 ` [PATCH v6 12/16] KVM: x86/pmu: Move pmc_speculative_in_use() to arch/x86/kvm/pmu.h Like Xu
2021-05-11 2:42 ` [PATCH v6 13/16] KVM: x86/pmu: Disable guest PEBS temporarily in two rare situations Like Xu
2021-05-11 2:42 ` [PATCH v6 14/16] KVM: x86/pmu: Add kvm_pmu_cap to optimize perf_get_x86_pmu_capability Like Xu
2021-05-11 2:42 ` [PATCH v6 15/16] KVM: x86/cpuid: Refactor host/guest CPU model consistency check Like Xu
2021-05-11 2:42 ` [PATCH v6 16/16] KVM: x86/pmu: Expose CPUIDs feature bits PDCM, DS, DTES64 Like Xu
2021-05-15 10:30 ` [PATCH v6 00/16] KVM: x86/pmu: Add *basic* support to enable guest PEBS via DS Liuxiangdong
2021-05-17 6:38 ` Like Xu
2021-05-18 12:23 ` Liuxiangdong
2021-05-18 12:40 ` Xu, Like
2021-05-18 13:15 ` Liuxiangdong
2021-05-19 1:44 ` Liuxiangdong
2021-05-21 1:37 ` Like Xu
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