Re: [PATCH v16 12/13] x86/tsc: Switch to native sched clock

Borislav Petkov
2025-01-08T08:22:49Z

On Wed, Jan 08, 2025 at 10:50:13AM +0530, Nikunj A. Dadhania wrote:
> All guests(including STSC) running on KVM or other hypervisors like Xen/VMWare
> uses the regular TSC when the guest is booted with TscInvariant bit set. But it
> doesn't switch the sched clock to use TSC which it should have, pointed here[1]
> by Sean:

Well, that paravirt_set_sched_clock() thing is there for a reason and all the
different guest types which call it perhaps have their reasons.

Now, if you think it would make sense to use the TSC in every guest type if
the TSC is this and that, then I'd need to see a patch or even a patchset
which explains why it is ok to do so on every guest type and then tested on
every guest type and then each patch would convert a single guest type and
properly explain why.

And your patch doesn't have that at all. I know Sean thinks it is a good idea
and perhaps it is but without proper justification and acks from the other
guest type maintainers, I simply won't take such a patch(-set).

And even if it is good, you need to solve it another way - not with this
delayed-work hackery.

IOW, this switching the paravirt clock crap to use TSC when the TSC is this
and that and the HV tells you so, should be a wholly separate patchset with
reviews and acks and the usual shebang.

If you want to take care only of STSC now, I'd take a patch which is known
good and tested properly. And that should happen very soon because the merge
window is closing in. Otherwise, there's always another merge window and
rushing things doesn't do any good anyway, as I keep preaching...

Your call.

--
Regards/Gruss,
Boris.