Re: [PATCH V7 00/18] KVM: x86/pmu: Add *basic* support to enable guest PEBS via DS

[Zhu, Lingshan]

On 6/28/2021 3:49 PM, Wang, Wei W wrote:
> On Friday, June 25, 2021 5:46 PM, Zhu, Lingshan wrote:
> > > Only on the host?
> > > I cannot use pebs unless try with "echo 0 > /proc/sys/kernel/watchdog"
> > > both on the host and guest on ICX.
> > Hi Xiangdong
> >
> > I guess you may run into the "cross-map" case(slow path below), so I think you
> > can disable them both in host and guest to make PEBS work.
> Hi Lingshan, could we also reproduce this issue?
>
> If the guest's watchdog takes away the virtual fixed counter, this will schedule the guest PEBS to use virtual PMC0. With the fast path (1:1 mapping), I think physical PMC0 is likely to be available for the guest PEBS emulation if no other host perf events are running.
I think it is possible, even a virtual counter need a perf event 
scheduled on the host. This depends on the guest / host workloads.

Thanks,
Zhu Lingshan
> Best,
> Wei