On Mon, Jul 29, 2019 at 09:23:38AM -0700, Sean Christopherson wrote:
> On Mon, Jul 29, 2019 at 01:32:43PM +0800, Peter Xu wrote:
> > The PLE window tracepoint triggers easily and it can be a bit
> > confusing too. One example line:
> >
> > kvm_ple_window: vcpu 0: ple_window 4096 (shrink 4096)
> >
> > It easily let people think of "the window now is 4096 which is
> > shrinked", but the truth is the value actually didn't change (4096).
> >
> > Let's only dump this message if the value really changed, and we make
> > the message even simpler like:
> >
> > kvm_ple_window: vcpu 4 (4096 -> 8192)
>
> This seems a bit too terse, e.g. requires a decent amount of effort to
> do relatively simple things like show only cases where the windows was
> shrunk, or grew/shrunk by a large amount. In this case, more is likely
> better, e.g.:
>
> kvm_ple_window_changed: vcpu 4 ple_window 8192 old 4096 grow 4096
>
> and
>
> kvm_ple_window_changed: vcpu 4 ple_window 4096 old 8192 shrink 4096
How about:
kvm_ple_window: vcpu 4 (4096 -> 8192, growed)
Or:
kvm_ple_window: vcpu 4 old 4096 new 8192 growed
I would prefer the arrow which is very clear to me to show a value
change, but I'd be fine to see what's your final preference or any
further reviewers. Anyway I think any of them is clearer than the
original version...
>
>
> Tangentially related, it'd be nice to settle on a standard format for
> printing field+val. Right now there are four different styles, e.g.
> "field=val", "field = val", "field: val" and "field val".
Right, I ses "field val" is used most frequently. But I didn't touch
those up because they haven't yet caused any confusion to me.
[...]
> > TP_STRUCT__entry(
> > - __field( bool, grow )
>
> Side note, if the tracepoint is invoked only on changes the "grow" field
> can be removed even if the tracepoint prints grow vs. shrink, i.e. there's
> no ambiguity since new==old will never happen.
But I do see it happen... Please see below.
>
> > __field( unsigned int, vcpu_id )
> > __field( int, new )
> > __field( int, old )
> > ),
> >
> > TP_fast_assign(
> > - __entry->grow = grow;
> > __entry->vcpu_id = vcpu_id;
> > __entry->new = new;
> > __entry->old = old;
> > ),
> >
> > - TP_printk("vcpu %u: ple_window %d (%s %d)",
> > - __entry->vcpu_id,
> > - __entry->new,
> > - __entry->grow ? "grow" : "shrink",
> > - __entry->old)
> > + TP_printk("vcpu %u (%d -> %d)",
> > + __entry->vcpu_id, __entry->old, __entry->new)
> > );
> >
> > -#define trace_kvm_ple_window_grow(vcpu_id, new, old) \
> > - trace_kvm_ple_window(true, vcpu_id, new, old)
> > -#define trace_kvm_ple_window_shrink(vcpu_id, new, old) \
> > - trace_kvm_ple_window(false, vcpu_id, new, old)
> > +#define trace_kvm_ple_window_changed(vcpu, new, old) \
> > + do { \
> > + if (old != new) \
> > + trace_kvm_ple_window(vcpu, new, old); \
> > + } while (0)
> >
> > TRACE_EVENT(kvm_pvclock_update,
> > TP_PROTO(unsigned int vcpu_id, struct pvclock_vcpu_time_info *pvclock),
> > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> > index d98eac371c0a..cc1f98130e6a 100644
> > --- a/arch/x86/kvm/vmx/vmx.c
> > +++ b/arch/x86/kvm/vmx/vmx.c
> > @@ -5214,7 +5214,7 @@ static void grow_ple_window(struct kvm_vcpu *vcpu)
> > if (vmx->ple_window != old)
> > vmx->ple_window_dirty = true;
> >
> > - trace_kvm_ple_window_grow(vcpu->vcpu_id, vmx->ple_window, old);
> > + trace_kvm_ple_window_changed(vcpu->vcpu_id, vmx->ple_window, old);
>
> No need for the macro, the snippet right about already checks 'new != old'.
> Though I do like the rename, i.e. rename the trace function to
> trace_kvm_ple_window_changed().
Do you mean this one?
if (vmx->ple_window != old)
vmx->ple_window_dirty = true;
It didn't return, did it? :)
Thanks,
--
Peter Xu
