Re: [PATCH] KVM: PPC: Book3S HV: Tracepoints for KVM HV guest interactions

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On Thu, 20 Nov 2014 13:10:12 +0100
Alexander Graf <agraf@xxxxxxx> wrote:

> 
> 
> On 20.11.14 11:40, Aneesh Kumar K.V wrote:
> > "Suresh E. Warrier" <warrier@xxxxxxxxxxxxxxxxxx> writes:
> > 
> >> This patch adds trace points in the guest entry and exit code and also
> >> for exceptions handled by the host in kernel mode - hypercalls and page
> >> faults. The new events are added to /sys/kernel/debug/tracing/events
> >> under a new subsystem called kvm_hv.
> > 
> > ........
> > 
> >>  	/* Set this explicitly in case thread 0 doesn't have a vcpu */
> >> @@ -1687,6 +1691,9 @@ static void kvmppc_run_core(struct kvmppc_vcore *vc)
> >>  
> >>  	vc->vcore_state = VCORE_RUNNING;
> >>  	preempt_disable();
> >> +
> >> +	trace_kvmppc_run_core(vc, 0);
> >> +
> >>  	spin_unlock(&vc->lock);
> > 
> > Do we really want to call tracepoint with spin lock held ? Is that a good
> > thing to do ?. 
> 
> I thought it was safe to call tracepoints inside of spin lock regions?
> Steve?
> 

There's tracepoints in the guts of the scheduler where rq lock is held.
Don't worry about it. The tracing system is lockless.

-- Steve
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