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

["Suresh E. Warrier" <warrier@linux.vnet.ibm.com>]

On 11/20/2014 08:01 AM, Steven Rostedt wrote:
> On Thu, 20 Nov 2014 13:10:12 +0100
> Alexander Graf <agraf@suse.de> wrote:
> 
>>
>>
>> On 20.11.14 11:40, Aneesh Kumar K.V wrote:
>>> "Suresh E. Warrier" <warrier@linux.vnet.ibm.com> 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.
> 

Thanks for confirming.

-suresh
 
> -- Steve
>