Re: [PATCH v5 08/24] sched: Introduce per memory space current virtual cpu id

[Sean Christopherson]

On Thu, Nov 17, 2022, Mathieu Desnoyers wrote:
> On 2022-11-17 14:10, Sean Christopherson wrote:
> > On Thu, Nov 17, 2022, Mathieu Desnoyers wrote:
> > > On 2022-11-14 15:49, Sean Christopherson wrote:
> > > > On Fri, Nov 11, 2022, Mathieu Desnoyers wrote:
> > > > > On 2022-11-10 23:41, Andy Lutomirski wrote:
> > > > > > On Thu, Nov 3, 2022 at 1:05 PM Mathieu Desnoyers
> > > > > > <mathieu.desnoyers@xxxxxxxxxxxx> wrote:
> > > > > > Also, in my mind "virtual cpu" is vCPU, which this isn't.  Maybe
> > > > > > "compacted cpu" or something?  It's a strange sort of concept.
> > > > > 
> > > > > I've kept the same wording that has been introduced in 2011 by Paul Turner
> > > > > and used internally at Google since then, although it may be confusing if
> > > > > people expect kvm-vCPU and rseq-vcpu to mean the same thing. Both really end
> > > > > up providing the semantic of a virtually assigned cpu id (in opposition to
> > > > > the logical cpu id on the system), but this is much more involved in the
> > > > > case of KVM.
> > > > 
> > > > I had the same reaction as Andy.  The rseq concepts don't worry me so much as the
> > > > existence of "vcpu" in mm_struct/task_struct, e.g. switch_mm_vcpu() when switching
> > > > between KVM vCPU tasks is going to be super confusing.  Ditto for mm_vcpu_get()
> > > > and mm_vcpu_put() in the few cases where KVM currently does mmget()/mmput().
> > > 
> > > I'm fine with changing the wording if it helps make things less confusing.
> > > 
> > > Should we go for "compact-cpu-id" ? "packed-cpu-id" ? Other ideas ?
> > 
> > What about something like "process-local-cpu-id" to capture that the ID has meaning
> > only within the associated address space / process?
> 
> Considering that the shorthand for "memory space" is "VM" in e.g. "CLONE_VM"

No objection from me for "vm", I've already had to untrain myself and remember
that "vm" doesn't always mean "virtual machine" :-)

> clone(2) flags, perhaps "vm-cpu-id", "vm-local-cpu-id" or "per-vm-cpu-id" ?

I have a slight preference for vm-local-cpu-id, but any of 'em work for me.