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
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".
>
> Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
> ---
> arch/x86/kvm/svm.c | 8 ++++----
> arch/x86/kvm/trace.h | 22 +++++++++-------------
> arch/x86/kvm/vmx/vmx.c | 4 ++--
> 3 files changed, 15 insertions(+), 19 deletions(-)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 48c865a4e5dd..0d365b621b5a 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -1268,8 +1268,8 @@ static void grow_ple_window(struct kvm_vcpu *vcpu)
> if (control->pause_filter_count != old)
> mark_dirty(svm->vmcb, VMCB_INTERCEPTS);
>
> - trace_kvm_ple_window_grow(vcpu->vcpu_id,
> - control->pause_filter_count, old);
> + trace_kvm_ple_window_changed(vcpu->vcpu_id,
> + control->pause_filter_count, old);
> }
>
> static void shrink_ple_window(struct kvm_vcpu *vcpu)
> @@ -1286,8 +1286,8 @@ static void shrink_ple_window(struct kvm_vcpu *vcpu)
> if (control->pause_filter_count != old)
> mark_dirty(svm->vmcb, VMCB_INTERCEPTS);
>
> - trace_kvm_ple_window_shrink(vcpu->vcpu_id,
> - control->pause_filter_count, old);
> + trace_kvm_ple_window_changed(vcpu->vcpu_id,
> + control->pause_filter_count, old);
> }
>
> static __init int svm_hardware_setup(void)
> diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
> index 76a39bc25b95..91c91f358b23 100644
> --- a/arch/x86/kvm/trace.h
> +++ b/arch/x86/kvm/trace.h
> @@ -891,34 +891,30 @@ TRACE_EVENT(kvm_pml_full,
> );
>
> TRACE_EVENT(kvm_ple_window,
> - TP_PROTO(bool grow, unsigned int vcpu_id, int new, int old),
> - TP_ARGS(grow, vcpu_id, new, old),
> + TP_PROTO(unsigned int vcpu_id, int new, int old),
> + TP_ARGS(vcpu_id, new, old),
>
> 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.
> __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().
> }
>
> static void shrink_ple_window(struct kvm_vcpu *vcpu)
> @@ -5229,7 +5229,7 @@ static void shrink_ple_window(struct kvm_vcpu *vcpu)
> if (vmx->ple_window != old)
> vmx->ple_window_dirty = true;
>
> - trace_kvm_ple_window_shrink(vcpu->vcpu_id, vmx->ple_window, old);
> + trace_kvm_ple_window_changed(vcpu->vcpu_id, vmx->ple_window, old);
> }
>
> /*
> --
> 2.21.0
>
