From: Andi Kleen <ak@linux.intel.com>
To: "Wang, Wei W" <wei.w.wang@intel.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"pbonzini@redhat.com" <pbonzini@redhat.com>,
"Liang, Kan" <kan.liang@intel.com>,
"peterz@infradead.org" <peterz@infradead.org>,
"mingo@redhat.com" <mingo@redhat.com>,
"rkrcmar@redhat.com" <rkrcmar@redhat.com>,
"Xu, Like" <like.xu@intel.com>
Subject: Re: [PATCH v2 6/8] perf/x86/intel/lbr: guest requesting KVM for lbr stack save/restore
Date: Fri, 7 Sep 2018 13:05:10 -0700 [thread overview]
Message-ID: <20180907200510.GR27886@tassilo.jf.intel.com> (raw)
In-Reply-To: <286AC319A985734F985F78AFA26841F73978F75E@shsmsx102.ccr.corp.intel.com>
> How would you realize the function of saving/restoring the lbr stack on the host?
>
> Here, we create a perf event on the host (please see guest_lbr_event_create on patch 7), which essentially satisfies all the conditions (e.g. increases cpuc->lbr_users) that are required to have the lbr stack saved/restored on the vCPU switching.
>
> If we want to stop the host side lbr stack save/restore for the vCPU, we need accordingly to call guest_lbr_event_release (in patch 7) to destroy that perf event (the host doesn't automatically stop saving the lbr stack for the vCPU if that perf event is still there).
>
> When would you call that release function? (we all know that the lbr doesn't need to be saved when the guest is not using it, but we need to destroy that perf event to achieve "doesn't need to be saved")
Maybe set a timer on DEBUGCTL LBR=0 ? A timer would provide hysteresis, so that quick toggles
(like in a PMI handler) wouldn't do anything expensive.
It needs new interfaces for perf anyways because we need to access the LBR state from
the last save.
-Andi
next prev parent reply other threads:[~2018-09-07 20:05 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-06 11:30 [PATCH v2 0/8] Guest LBR Enabling Wei Wang
2018-09-06 11:30 ` [PATCH v2 1/8] perf/x86: add a function to get the lbr stack Wei Wang
2018-09-07 3:28 ` Andi Kleen
2018-09-07 6:45 ` Wei Wang
2018-09-06 11:30 ` [PATCH v2 2/8] KVM/x86: KVM_CAP_X86_GUEST_LBR Wei Wang
2018-09-06 11:30 ` [PATCH v2 3/8] KVM/vmx: Pass through the lbr stack to a guest Wei Wang
2018-09-06 11:30 ` [PATCH v2 4/8] KVM/x86: expose MSR_IA32_PERF_CAPABILITIES to the guest Wei Wang
2018-09-06 11:30 ` [PATCH v2 5/8] KVM/x86: enable the guest to access the debugctl msr Wei Wang
2018-09-06 11:30 ` [PATCH v2 6/8] perf/x86/intel/lbr: guest requesting KVM for lbr stack save/restore Wei Wang
2018-09-07 3:27 ` Andi Kleen
2018-09-07 5:24 ` Wei Wang
2018-09-07 14:10 ` Andi Kleen
2018-09-07 15:20 ` Wang, Wei W
2018-09-07 20:05 ` Andi Kleen [this message]
2018-09-08 1:34 ` Wang, Wei W
2018-09-06 11:30 ` [PATCH v2 7/8] KVM: PMU: support to save/restore the guest lbr stack on vCPU switching Wei Wang
2018-09-07 14:36 ` Jann Horn
2018-09-07 15:21 ` Wang, Wei W
2018-09-18 0:58 ` Gonglei (Arei)
2018-09-18 2:56 ` Andi Kleen
2018-09-18 9:57 ` Wei Wang
2018-09-18 10:34 ` Gonglei (Arei)
2018-09-06 11:30 ` [PATCH v2 8/8] perf/x86/intel/lbr: add the guest_lbr boolean to cpuc Wei Wang
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