From: Peter Zijlstra <peterz@infradead.org>
To: Wei Wang <wei.w.wang@intel.com>
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: Tue, 9 Jul 2019 13:45:54 +0200 [thread overview]
Message-ID: <20190709114554.GW3402@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <1562548999-37095-9-git-send-email-wei.w.wang@intel.com>
On Mon, Jul 08, 2019 at 09:23:15AM +0800, Wei Wang wrote:
> +int intel_pmu_enable_save_guest_lbr(struct kvm_vcpu *vcpu)
> +{
> + struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
> + struct perf_event *event;
> +
> + /*
> + * The main purpose of this perf event is to have the host perf core
> + * help save/restore the guest lbr stack on vcpu switching. There is
> + * no perf counters allocated for the event.
> + *
> + * About the attr:
> + * exclude_guest: set to true to indicate that the event runs on the
> + * host only.
That's a lie; it _never_ runs. You specifically don't want the host to
enable LBR so as not to corrupt the guest state.
> + * pinned: set to false, so that the FLEXIBLE events will not
> + * be rescheduled for this event which actually doesn't
> + * need a perf counter.
Unparsable gibberish. Specifically by making it flexible it is
susceptible to rotation and there's no guarantee it will actually get
scheduled.
> + * 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?
> + * 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?
> + */
> + struct perf_event_attr attr = {
> + .type = PERF_TYPE_RAW,
> + .size = sizeof(attr),
> + .exclude_guest = true,
> + .pinned = false,
> + .config = 0,
> + .sample_period = 0,
> + .sample_type = PERF_SAMPLE_BRANCH_STACK,
> + .branch_sample_type = PERF_SAMPLE_BRANCH_CALL_STACK |
> + PERF_SAMPLE_BRANCH_USER,
> + };
> +
> + if (pmu->vcpu_lbr_event)
> + return 0;
> +
> + event = perf_event_create(&attr, -1, current, NULL, NULL, false);
> + if (IS_ERR(event)) {
> + pr_err("%s: failed %ld\n", __func__, PTR_ERR(event));
> + return -ENOENT;
> + }
> + pmu->vcpu_lbr_event = event;
> +
> + return 0;
> +}
next prev parent reply other threads:[~2019-07-09 11:46 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 [this message]
2019-07-10 8:21 ` Wei Wang
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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