Re: kvm mmu tracing quirks

[Avi Kivity <avi@redhat.com>]

On 04/13/2011 05:09 PM, Jan Kiszka wrote:
> Hi Xiao,
>
> while tracing a guest with all events enabled, I notices some issues
> with kvm mmu instrumentations. A critical one:
>
> TRACE_EVENT(
> 	kvm_mmu_audit,
> 	TP_PROTO(struct kvm_vcpu *vcpu, int audit_point),
> 	TP_ARGS(vcpu, audit_point),
>
> 	TP_STRUCT__entry(
> 		__field(struct kvm_vcpu *, vcpu)
> 		__field(int, audit_point)
> 	),
>
> 	TP_fast_assign(
> 		__entry->vcpu = vcpu;
> 		__entry->audit_point = audit_point;
> 	),
>
> 	TP_printk("vcpu:%d %s", __entry->vcpu->cpu,
> 		  audit_point_name[__entry->audit_point])
> );
>
> Saving the vcpu reference to the trace buffer can break on dump if the
> vcpu was destroyed in the meantime. I was about to fix that by saving
> vcpu->cpu instead, but then I wondered what kind of information you
> actually need here. The triggering host cpu is automatically recorded by
> ftrace anyway. Can you comment on this / clean it up? Also, it would be
> nice to use __print_symbolic for translating audit_point to a string as
> that would also work for trace-cmd/kernelshark.
>

IIRC the audit trace is only used to get a low cost invocation for the 
audit machinery; it's not actually useful as a user tracepoint.

We should probably switch to static_branch() instead 
(https://lwn.net/Articles/429447/).

-- 
error compiling committee.c: too many arguments to function