Re: [PATCH v5 1/4] KVM: stats: Separate common stats from architecture specific ones

Jing Zhang
2021-05-18T17:25:40Z

Hi David,

On Tue, May 18, 2021 at 11:27 AM David Matlack <dmatlack@google.com> wrote:
>
> On Mon, May 17, 2021 at 5:10 PM Jing Zhang <jingzhangos@google.com> wrote:
> <snip>
> > Actually the definition of kvm_{vcpu,vm}_stat are arch specific. There is
> > no real structure for arch agnostic stats. Most of the stats in common
> > structures are arch agnostic, but not all of them.
> > There are some benefits to put all common stats in a separate structure.
> > e.g. if we want to add a stat in kvm_main.c, we only need to add this stat
> > in the common structure, don't have to update all kvm_{vcpu,vm}_stat
> > definition for all architectures.
>
> I meant rename the existing arch-specific struct kvm_{vcpu,vm}_stat to
> kvm_{vcpu,vm}_stat_arch and rename struct kvm_{vcpu,vm}_stat_common to
> kvm_{vcpu,vm}_stat.
>
> So in include/linux/kvm_types.h you'd have:
>
> struct kvm_vm_stat {
> ulong remote_tlb_flush;
> struct kvm_vm_stat_arch arch;
> };
>
> struct kvm_vcpu_stat {
> u64 halt_successful_poll;
> u64 halt_attempted_poll;
> u64 halt_poll_invalid;
> u64 halt_wakeup;
> u64 halt_poll_success_ns;
> u64 halt_poll_fail_ns;
> struct kvm_vcpu_stat_arch arch;
> };
>
> And in arch/x86/include/asm/kvm_host.h you'd have:
>
> struct kvm_vm_stat_arch {
> ulong mmu_shadow_zapped;
> ...
> };
>
> struct kvm_vcpu_stat_arch {
> u64 pf_fixed;
> u64 pf_guest;
> u64 tlb_flush;
> ...
> };
>
> You still have the same benefits of having an arch-neutral place to
> store stats but the struct layout more closely resembles struct
> kvm_vcpu and struct kvm.
You are right. This is a more reasonable way to layout the structures.
I remember that I didn't choose this way is only because that it needs
touching every arch specific stats in all architectures (stat.name ->
stat.arch.name) instead of only touching arch neutral stats.
Let's see if there is any vote from others about this.

Thanks,
Jing