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From: "Liang, Kan" <kan.liang@linux.intel.com>
To: Wei Wang <wei.w.wang@intel.com>,
	linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	pbonzini@redhat.com, ak@linux.intel.com, peterz@infradead.org
Cc: kan.liang@intel.com, mingo@redhat.com, rkrcmar@redhat.com,
	like.xu@intel.com, jannh@google.com, arei.gonglei@huawei.com
Subject: Re: [PATCH v4 04/10] KVM/x86: intel_pmu_lbr_enable
Date: Wed, 2 Jan 2019 11:33:06 -0500	[thread overview]
Message-ID: <5a04d8ea-b788-6018-8b34-ebd528578916@linux.intel.com> (raw)
In-Reply-To: <1545816338-1171-5-git-send-email-wei.w.wang@intel.com>



On 12/26/2018 4:25 AM, Wei Wang wrote:
> +
> +	/*
> +	 * It could be possible that people have vcpus of old model run on
> +	 * physcal cpus of newer model, for example a BDW guest on a SKX
> +	 * machine (but not possible to be the other way around).
> +	 * The BDW guest may not get accurate results on a SKX machine as it
> +	 * only reads 16 entries of the lbr stack while there are 32 entries
> +	 * of recordings. So we currently forbid the lbr enabling when the
> +	 * vcpu and physical cpu see different lbr stack entries.

I think it's not enough to only check number of entries. The LBR from/to 
MSRs may be different even the number of entries is the same, e.g SLM 
and KNL.

> +	 */
> +	switch (vcpu_model) {

That's a duplicate of intel_pmu_init(). I think it's better to factor 
out the common part if you want to check LBR MSRs and entries. Then we 
don't need to add the same codes in two different places when enabling 
new platforms.

Actually, I think we may just support LBR for guest if it has the 
identical CPU model as host. It should be good enough for now.

Thanks,
Kan
> +	case INTEL_FAM6_CORE2_MEROM:
> +	case INTEL_FAM6_CORE2_MEROM_L:

  reply	other threads:[~2019-01-02 16:33 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-26  9:25 [PATCH v4 00/10] Guest LBR Enabling Wei Wang
2018-12-26  9:25 ` [PATCH v4 01/10] perf/x86: fix the variable type of the LBR MSRs Wei Wang
2018-12-26  9:25 ` [PATCH v4 02/10] perf/x86: add a function to get the lbr stack Wei Wang
2018-12-26  9:25 ` [PATCH v4 03/10] KVM/x86: KVM_CAP_X86_GUEST_LBR Wei Wang
2018-12-26  9:25 ` [PATCH v4 04/10] KVM/x86: intel_pmu_lbr_enable Wei Wang
2019-01-02 16:33   ` Liang, Kan [this message]
2019-01-04  9:58     ` Wei Wang
2019-01-04 15:57       ` Liang, Kan
2019-01-05 10:09         ` Wei Wang
2019-01-07 14:22           ` Liang, Kan
2019-01-08  6:13             ` Wei Wang
2019-01-08 14:08               ` Liang, Kan
2019-01-09  1:54                 ` Wei Wang
2019-01-02 23:26   ` Jim Mattson
2019-01-03  7:22     ` Wei Wang
2019-01-03 15:34       ` Jim Mattson
2019-01-03 17:18         ` Andi Kleen
2019-01-04 10:09         ` Wei Wang
2019-01-04 15:53           ` Jim Mattson
2019-01-05 10:15             ` Wang, Wei W
2018-12-26  9:25 ` [PATCH v4 05/10] KVM/x86: expose MSR_IA32_PERF_CAPABILITIES to the guest Wei Wang
2019-01-02 23:40   ` Jim Mattson
2019-01-03  8:00     ` Wei Wang
2019-01-03 15:25       ` Jim Mattson
2019-01-07  9:15         ` Wei Wang
2019-01-07 18:05           ` Jim Mattson
2019-01-07 18:20             ` Andi Kleen
2019-01-07 18:48               ` Jim Mattson
2019-01-07 20:14                 ` Andi Kleen
2019-01-07 21:00                   ` Jim Mattson
2019-01-08  7:53                 ` Wei Wang
2019-01-08 17:19                   ` Jim Mattson
2018-12-26  9:25 ` [PATCH v4 06/10] perf/x86: no counter allocation support Wei Wang
2018-12-26  9:25 ` [PATCH v4 07/10] KVM/x86/vPMU: Add APIs to support host save/restore the guest lbr stack Wei Wang
2018-12-26  9:25 ` [PATCH v4 08/10] perf/x86: save/restore LBR_SELECT on vCPU switching Wei Wang
2018-12-26  9:25 ` [PATCH v4 09/10] perf/x86: function to check lbr user callstack mode Wei Wang
2018-12-26  9:25 ` [PATCH v4 10/10] KVM/x86/lbr: lazy save the guest lbr stack Wei Wang
2018-12-27 20:51   ` Andi Kleen
2018-12-28  3:47     ` Wei Wang
2018-12-28 19:10       ` Andi Kleen
2018-12-27 20:52   ` [PATCH v4 10/10] KVM/x86/lbr: lazy save the guest lbr stack II Andi Kleen
2018-12-29  4:25     ` Wang, Wei W

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