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: Mon, 8 Jul 2019 16:48:31 +0200 [thread overview]
Message-ID: <20190708144831.GN3402@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:
> From: Like Xu <like.xu@intel.com>
>
> This patch adds support to enable/disable the host side save/restore
This patch should be disqualified on Changelog alone...
Documentation/process/submitting-patches.rst:instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy
> for the guest lbr stack on vCPU switching. To enable that, the host
> creates a perf event for the vCPU, and the event attributes are set
> to the user callstack mode lbr so that all the conditions are meet in
> the host perf subsystem to save the lbr stack on task switching.
>
> The host side lbr perf event are created only for the purpose of saving
> and restoring the lbr stack. There is no need to enable the lbr
> functionality for this perf event, because the feature is essentially
> used in the vCPU. So perf_event_create is invoked with need_counter=false
> to get no counter assigned for the perf event.
>
> The vcpu_lbr field is added to cpuc, to indicate if the lbr perf event is
> used by the vCPU only for context switching. When the perf subsystem
> handles this event (e.g. lbr enable or read lbr stack on PMI) and finds
> it's non-zero, it simply returns.
*WHY* does the host need to save/restore? Why not make VMENTER/VMEXIT do
this?
Many of these patches don't explain why things are done; that's a
problem.
next prev parent reply other threads:[~2019-07-08 14:48 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 [this message]
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
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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