Re: [PATCH] perf/intel: Remove Perfmon-v4 counter_freezing support

[Paolo Bonzini]

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@xxxxxxxxxxxxx>  
> > 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