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

Zhu, Lingshan
2021-06-28T07:53:51Z

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