Messages in this thread | | | Subject | Re: [PATCH] perf/intel: Remove Perfmon-v4 counter_freezing support | From | "Xu, Like" <> | Date | Tue, 26 Jan 2021 19:35:03 +0800 |
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On 2021/1/26 17:51, Paolo Bonzini wrote: > On 11/11/20 03:42, Xu, Like wrote: >> Hi Peter, >> >> On 2020/11/11 4:52, Stephane Eranian wrote: >>> On Tue, Nov 10, 2020 at 7:37 AM Peter Zijlstra<peterz@infradead.org> >>> wrote: >>>> On Tue, Nov 10, 2020 at 04:12:57PM +0100, Peter Zijlstra wrote: >>>>> On Mon, Nov 09, 2020 at 10:12:37AM +0800, Like Xu wrote: >>>>>> The Precise Event Based Sampling(PEBS) supported on Intel Ice Lake >>>>>> server >>>>>> platforms can provide an architectural state of the instruction >>>>>> executed >>>>>> after the instruction that caused the event. This patch set enables the >>>>>> the PEBS via DS feature for KVM (also non) Linux guest on the Ice Lake. >>>>>> The Linux guest can use PEBS feature like native: >>>>>> >>>>>> # perf record -e instructions:ppp ./br_instr a >>>>>> # perf record -c 100000 -e instructions:pp ./br_instr a >>>>>> >>>>>> If the counter_freezing is not enabled on the host, the guest PEBS will >>>>>> be disabled on purpose when host is using PEBS facility. By default, >>>>>> KVM disables the co-existence of guest PEBS and host PEBS. >> Thanks Stephane for clarifying the use cases for Freeze-on-[PMI|Overflow]. >> >> Please let me express it more clearly. >> >> The goal of the whole patch set is to enable guest PEBS, regardless of >> whether the counter_freezing is frozen or not. By default, it will not >> support both the guest and the host to use PEBS at the same time. >> >> Please continue reviewing the patch set, especially for the slow path >> we proposed this time and related host perf changes: >> >> - add intel_pmu_handle_guest_pebs() to __intel_pmu_pebs_event(); >> - add switch MSRs (PEBS_ENABLE, DS_AREA, DATA_CFG) to >> intel_guest_get_msrs(); >> - the construction of incoming parameters for >> perf_event_create_kernel_counter(); >> >> I believe if you understand the general idea, the comments will be very >> valuable. > > What is the state of this work? I was expecting a new version that > doesn't use counter_freezing. However, I see that counter_freezing is > still in there, so this patch from Peter has never been applied. > > Paolo
Ah, now we have the v3 version on guest PEBS feature. It does not rely on counter_freezing, but disables the co-existence of guest PEBS and host PEBS. I am not clear about your attitude towards this co-existence.
There are also more interesting topics for you to review and comment. Please check https://lore.kernel.org/kvm/20210104131542.495413-1-like.xu@linux.intel.com/
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