From: Wei Wang <wei.w.wang@intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
pbonzini@redhat.com, ak@linux.intel.com, kan.liang@intel.com,
mingo@redhat.com, rkrcmar@redhat.com, like.xu@intel.com,
jannh@google.com, arei.gonglei@huawei.com, jmattson@google.com
Subject: Re: [PATCH v7 08/12] KVM/x86/vPMU: Add APIs to support host save/restore the guest lbr stack
Date: Wed, 10 Jul 2019 16:21:45 +0800 [thread overview]
Message-ID: <5D25A019.6080708@intel.com> (raw)
In-Reply-To: <20190709114554.GW3402@hirez.programming.kicks-ass.net>
On 07/09/2019 07:45 PM, Peter Zijlstra wrote:
>
>> + * config: Actually this field won't be used by the perf core
>> + * as this event doesn't have a perf counter.
>> + * sample_period: Same as above.
> If it's unused; why do we need to set it at all?
OK, we'll remove the unused fields.
>
>> + * sample_type: tells the perf core that it is an lbr event.
>> + * branch_sample_type: tells the perf core that the lbr event works in
>> + * the user callstack mode so that the lbr stack will be
>> + * saved/restored on vCPU switching.
> Again; doesn't make sense. What does the user part have to do with
> save/restore? What happens when this vcpu thread drops to userspace for
> an assist?
This is a fake event which doesn't run the lbr on the host.
Returning to userspace doesn't need save/restore lbr, because userspace
wouldn't change those lbr msrs.
The event is created to save/restore lbr msrs on vcpu switching.
Host perf only do this save/restore for "user callstack mode" lbr event,
so we
construct the event to be "user callstack mode" to reuse the host lbr
save/restore.
An alternative method is to have KVM vcpu sched_in/out callback
save/restore those msrs, which don't need to create this fake event.
Please let me know if you prefer the second method.
Best,
Wei
next prev parent reply other threads:[~2019-07-10 8:16 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-08 1:23 [PATCH v7 00/12] Guest LBR Enabling Wei Wang
2019-07-08 1:23 ` [PATCH v7 01/12] perf/x86: fix the variable type of the LBR MSRs Wei Wang
2019-07-08 1:23 ` [PATCH v7 02/12] perf/x86: add a function to get the lbr stack Wei Wang
2019-07-08 1:23 ` [PATCH v7 03/12] KVM/x86: KVM_CAP_X86_GUEST_LBR Wei Wang
2019-07-08 1:23 ` [PATCH v7 04/12] KVM/x86: intel_pmu_lbr_enable Wei Wang
2019-07-08 1:23 ` [PATCH v7 05/12] KVM/x86/vPMU: tweak kvm_pmu_get_msr Wei Wang
2019-07-08 1:23 ` [PATCH v7 06/12] KVM/x86: expose MSR_IA32_PERF_CAPABILITIES to the guest Wei Wang
2019-07-08 1:23 ` [PATCH v7 07/12] perf/x86: no counter allocation support Wei Wang
2019-07-08 14:29 ` Peter Zijlstra
2019-07-09 2:58 ` Wei Wang
2019-07-09 9:43 ` Peter Zijlstra
2019-07-09 11:36 ` Wei Wang
2019-07-08 1:23 ` [PATCH v7 08/12] KVM/x86/vPMU: Add APIs to support host save/restore the guest lbr stack Wei Wang
2019-07-08 14:48 ` Peter Zijlstra
2019-07-09 3:04 ` Wei Wang
2019-07-09 9:39 ` Peter Zijlstra
2019-07-09 11:34 ` Wei Wang
2019-07-09 12:19 ` Peter Zijlstra
2019-07-10 8:19 ` Wei Wang
2019-07-09 11:45 ` Peter Zijlstra
2019-07-10 8:21 ` Wei Wang [this message]
2019-07-08 1:23 ` [PATCH v7 09/12] perf/x86: save/restore LBR_SELECT on vCPU switching Wei Wang
2019-07-08 1:23 ` [PATCH v7 10/12] KVM/x86/lbr: lazy save the guest lbr stack Wei Wang
2019-07-08 14:53 ` Peter Zijlstra
2019-07-08 15:11 ` Andi Kleen
2019-07-09 11:39 ` Peter Zijlstra
2019-07-09 3:14 ` Wei Wang
2019-07-08 1:23 ` [PATCH v7 11/12] KVM/x86: remove the common handling of the debugctl msr Wei Wang
2019-07-08 1:23 ` [PATCH v7 12/12] KVM/VMX/vPMU: support to report GLOBAL_STATUS_LBRS_FROZEN Wei Wang
2019-07-08 15:09 ` Peter Zijlstra
2019-07-09 3:24 ` Wei Wang
2019-07-09 11:35 ` Peter Zijlstra
2019-07-10 9:23 ` Wei Wang
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