Re: Xen timecounter issues

["Mathew, Cherry G." <c%bow.st@localhost>]

>>>>> On Mon, 24 Jun 2024 11:48:50 +0200, Manuel Bouyer <bouyer%antioche.eu.org@localhost> said:

> On Mon, Jun 24, 2024 at 09:39:32AM +0000, Mathew, Cherry G. wrote:
>> >>>>> On Mon, 24 Jun 2024 11:30:14 +0200, Manuel Bouyer <bouyer%antioche.eu.org@localhost> said:
>> 
>> [...]
>> 
>> >> else if ( pv_shim && v->vcpu_id == 0 )
>> >> {
>> >> /*
>> >> * PV-shim: vcpus are pinned 1:1. Initially only 1 cpu is online,
>> >> * others will be dealt with when onlining them. This avoids pinning
>> >> * a vcpu to a not yet online cpu here.
>> >> */
>> >> sched_set_affinity(unit, cpumask_of(0), cpumask_of(0));
>> 
>> [...]
>> 
>> 
>> > But this doens't tell anything about CPU 0 ?
>> 
>> It does - that's the first part of the if clause. So in the UP case,
>> vcpu0 is pinned to pcpu0 - which is probably why this doesn't show up in
>> the dom0/UP case.

> The first part of the if clause is about pv_shim, which is not in use for dom0
> AFAIK the part of the if clause will be taken only for domUs started with
> type="pvh"
> pvshim=1

> and this will never be the case for dom0

Oh, I assumed that pvshim was for PV hypervisor emulation (not sure why
I got that impression).

This opens up the question of why the TSC bug doesn't appear in the
dom0/UP case, without explicit vCPU pinning then.

-- 
Math/(~cherry)