Re: [PATCH V2 03/11] perf/x86: Add support for TSC in nanoseconds as a perf event clock

From: Adrian Hunter
Date: Tue Apr 26 2022 - 02:52:07 EST

On 25/04/22 20:05, Thomas Gleixner wrote:
> On Mon, Apr 25 2022 at 16:15, Adrian Hunter wrote:
>> On 25/04/22 12:32, Thomas Gleixner wrote:
>>> It's hillarious, that we still cling to this pvclock abomination, while
>>> we happily expose TSC deadline timer to the guest. TSC virt scaling was
>>> implemented in hardware for a reason.
>> So you are talking about changing VMX TCS Offset on every VM-Entry to try to hide
>> the time jumps when the VM is scheduled out? Or neglect that and just let the time
>> jumps happen?
>> If changing VMX TCS Offset, how can TSC be kept consistent between each VCPU i.e.
>> wouldn't that mean each VCPU has to have the same VMX TSC Offset?
> Obviously so. That's the only thing which makes sense, no?

[ Sending this again, because I notice I messed up the email "From" ]

But wouldn't that mean changing all the VCPUs VMX TSC Offset at the same time,
which means when none are currently executing? How could that be done?