From: "Xu, Like" <like.xu@intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Like Xu <like.xu@linux.intel.com>,
Kan Liang <kan.liang@linux.intel.com>,
Paolo Bonzini <pbonzini@redhat.com>,
eranian@google.com, kvm@vger.kernel.org,
Ingo Molnar <mingo@redhat.com>,
Sean Christopherson <seanjc@google.com>,
Thomas Gleixner <tglx@linutronix.de>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
Andi Kleen <andi@firstfloor.org>,
wei.w.wang@intel.com, luwei.kang@intel.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 04/17] perf: x86/ds: Handle guest PEBS overflow PMI and inject it to guest
Date: Fri, 15 Jan 2021 22:30:13 +0800 [thread overview]
Message-ID: <2c197d5a-09a8-968c-a942-c95d18983c9d@intel.com> (raw)
In-Reply-To: <YAGEFgqQv281jVHc@hirez.programming.kicks-ass.net>
On 2021/1/15 20:01, Peter Zijlstra wrote:
> On Thu, Jan 14, 2021 at 11:39:00AM +0800, Xu, Like wrote:
>
>>> Why do we need to? Can't we simply always forward the PMI if the guest
>>> has bits set in MSR_IA32_PEBS_ENABLE ? Surely we can access the guest
>>> MSRs at a reasonable rate..
>>>
>>> Sure, it'll send too many PMIs, but is that really a problem?
>> More vPMI means more guest irq handler calls and
>> more PMI virtualization overhead.
> Only if you have both guest and host PEBS. And in that case I really
> can't be arsed about some overhead to the guest.
Less overhead makes everyone happier.
Ah, can I assume that you're fine with disabling the
co-existence of guest PEBS and host PEBS as the first upstream step ?
>
>> In addition,
>> the correctness of some workloads (RR?) depends on
>> the correct number of PMIs and the PMI trigger times
>> and virt may not want to break this assumption.
> Are you sure? Spurious NMI/PMIs are known to happen anyway. We have far
> too much code to deal with them.
https://lore.kernel.org/lkml/20170628130748.GI5981@leverpostej/T/
In the rr workload, the commit change "the PMI interrupts in skid region
should be dropped"
is reverted since some users complain that:
> It seems to me that it might be reasonable to ignore the interrupt if
> the purpose of the interrupt is to trigger sampling of the CPUs
> register state. But if the interrupt will trigger some other
> operation, such as a signal on an fd, then there's no reason to drop
> it.
I assume that if the PMI drop is unacceptable, either will spurious PMI
injection.
I'm pretty open if you insist that we really need to do this for guest PEBS
enabling.
>
>>>> + * If PEBS interrupt threshold on host is not exceeded in a NMI, there
>>>> + * must be a PEBS overflow PMI generated from the guest PEBS counters.
>>>> + * There is no ambiguity since the reported event in the PMI is guest
>>>> + * only. It gets handled correctly on a case by case base for each event.
>>>> + *
>>>> + * Note: KVM disables the co-existence of guest PEBS and host PEBS.
>>> Where; I need a code reference here.
>> How about:
>>
>> Note: KVM will disable the co-existence of guest PEBS and host PEBS.
>> In the intel_guest_get_msrs(), when we have host PEBS ctrl bit(s) enabled,
>> KVM will clear the guest PEBS ctrl enable bit(s) before vm-entry.
>> The guest PEBS users should be notified of this runtime restriction.
> Since you had me look at that function, can clean up that
> CONFIG_RETPOLINE crud and replace it with static_call() ?
Sure. Let me try it.
---
thx, likexu
next prev parent reply other threads:[~2021-01-15 14:31 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-04 13:15 [PATCH v3 00/17] KVM: x86/pmu: Add support to enable Guest PEBS via DS Like Xu
2021-01-04 13:15 ` [PATCH v3 01/17] KVM: x86/pmu: Set MSR_IA32_MISC_ENABLE_EMON bit when vPMU is enabled Like Xu
2021-01-04 13:15 ` [PATCH v3 02/17] KVM: x86/pmu: Use IA32_PERF_CAPABILITIES to adjust features visibility Like Xu
2021-01-04 13:15 ` [PATCH v3 03/17] KVM: x86/pmu: Introduce the ctrl_mask value for fixed counter Like Xu
2021-01-13 18:06 ` Peter Zijlstra
2021-01-14 1:58 ` Xu, Like
2021-01-04 13:15 ` [PATCH v3 04/17] perf: x86/ds: Handle guest PEBS overflow PMI and inject it to guest Like Xu
2021-01-13 18:22 ` Peter Zijlstra
2021-01-13 18:27 ` Peter Zijlstra
2021-01-14 3:39 ` Xu, Like
2021-01-15 12:01 ` Peter Zijlstra
2021-01-15 14:30 ` Xu, Like [this message]
2021-01-15 14:44 ` Peter Zijlstra
2021-01-15 15:12 ` Xu, Like
2021-01-25 8:26 ` Like Xu
2021-01-25 11:47 ` Peter Zijlstra
2021-02-02 6:31 ` Xu, Like
2021-01-14 18:55 ` Sean Christopherson
2021-01-15 2:49 ` Xu, Like
2021-01-15 17:42 ` Sean Christopherson
2021-01-22 5:30 ` Like Xu
2021-01-04 13:15 ` [PATCH v3 05/17] KVM: x86/pmu: Reprogram guest PEBS event to emulate guest PEBS counter Like Xu
2021-01-15 11:33 ` Peter Zijlstra
2021-01-15 13:53 ` Xu, Like
2021-01-04 13:15 ` [PATCH v3 06/17] KVM: x86/pmu: Add IA32_PEBS_ENABLE MSR emulation for extended PEBS Like Xu
2021-01-05 21:11 ` Sean Christopherson
2021-01-07 12:38 ` Xu, Like
2021-01-15 14:46 ` Peter Zijlstra
2021-01-15 15:29 ` Xu, Like
2021-01-04 13:15 ` [PATCH v3 07/17] KVM: x86/pmu: Add IA32_DS_AREA MSR emulation to manage guest DS buffer Like Xu
2021-01-05 21:16 ` Sean Christopherson
2021-01-08 3:05 ` Xu, Like
2021-01-04 13:15 ` [PATCH v3 08/17] KVM: x86/pmu: Add PEBS_DATA_CFG MSR emulation to support adaptive PEBS Like Xu
2021-01-04 13:15 ` [PATCH v3 09/17] KVM: x86: Set PEBS_UNAVAIL in IA32_MISC_ENABLE when PEBS is enabled Like Xu
2021-01-04 13:15 ` [PATCH v3 10/17] KVM: x86/pmu: Expose CPUIDs feature bits PDCM, DS, DTES64 Like Xu
2021-01-04 13:15 ` [PATCH v3 11/17] KVM: x86/pmu: Adjust precise_ip to emulate Ice Lake guest PDIR counter Like Xu
2021-01-04 13:15 ` [PATCH v3 12/17] KVM: x86/pmu: Disable guest PEBS when counters are cross-mapped Like Xu
2021-01-04 13:15 ` [PATCH v3 13/17] KVM: x86/pmu: Add hook to emulate pebs for cross-mapped counters Like Xu
2021-01-04 13:15 ` [PATCH v3 14/17] KVM: vmx/pmu: Limit pebs_interrupt_threshold in the guest DS area Like Xu
2021-01-04 13:15 ` [PATCH v3 15/17] KVM: vmx/pmu: Rewrite applicable_counters field in guest PEBS records Like Xu
2021-01-04 13:15 ` [PATCH v3 16/17] KVM: x86/pmu: Save guest pebs reset values when pebs is configured Like Xu
2021-01-04 13:15 ` [PATCH v3 17/17] KVM: x86/pmu: Adjust guest pebs reset values for crpss-mapped counters Like Xu
2021-01-14 19:10 ` [PATCH v3 00/17] KVM: x86/pmu: Add support to enable Guest PEBS via DS Sean Christopherson
2021-01-15 2:02 ` Xu, Like
2021-01-15 17:57 ` Sean Christopherson
2021-01-15 18:27 ` Andi Kleen
2021-01-15 18:51 ` Sean Christopherson
2021-01-15 19:11 ` Andi Kleen
2021-01-22 9:56 ` Peter Zijlstra
2021-01-25 8:08 ` Like Xu
2021-01-25 11:13 ` Peter Zijlstra
2021-01-25 12:07 ` Xu, Like
2021-01-25 12:18 ` Peter Zijlstra
2021-01-25 12:53 ` Xu, Like
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