linux-kernel - Re: [PATCH 8/9] perf kvm: debug for missing vmexit/vmentry event

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Message-ID: <51FFBE17.60409@gmail.com>
Date:	Mon, 05 Aug 2013 11:00:39 -0400
From:	David Ahern <dsahern@...il.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
CC:	acme@...stprotocols.net, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Runzhen Wang <runzhen@...ux.vnet.ibm.com>
Subject: Re: [PATCH 8/9] perf kvm: debug for missing vmexit/vmentry event

On 8/5/13 2:53 AM, Xiao Guangrong wrote:
> On 08/03/2013 04:05 AM, David Ahern wrote:
>> Expected to have missing events for each vcpu when perf is
>> started. After that should not have missing events.
>
> Sorry, i can not understand what's this info used for.

For debugging. Things that should not happen do seem to happen -- 
rarely, but it does

>
>>
>> Signed-off-by: David Ahern <dsahern@...il.com>
>> Cc: Arnaldo Carvalho de Melo <acme@...stprotocols.net>
>> Cc: Ingo Molnar <mingo@...nel.org>
>> Cc: Frederic Weisbecker <fweisbec@...il.com>
>> Cc: Peter Zijlstra <peterz@...radead.org>
>> Cc: Jiri Olsa <jolsa@...hat.com>
>> Cc: Namhyung Kim <namhyung@...nel.org>
>> Cc: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
>> Cc: Runzhen Wang <runzhen@...ux.vnet.ibm.com>
>> ---
>>   tools/perf/builtin-kvm.c |   15 +++++++++++++--
>>   1 file changed, 13 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/perf/builtin-kvm.c b/tools/perf/builtin-kvm.c
>> index 28afc05d..41dd25a 100644
>> --- a/tools/perf/builtin-kvm.c
>> +++ b/tools/perf/builtin-kvm.c
>> @@ -568,11 +568,22 @@ static bool handle_kvm_event(struct perf_kvm_stat *kvm,
>>   	    (kvm->trace_vcpu != vcpu_record->vcpu_id))
>>   		return true;
>>
>> -	if (kvm->events_ops->is_begin_event(evsel, sample, &key))
>> +	if (kvm->events_ops->is_begin_event(evsel, sample, &key)) {
>> +		if (vcpu_record->start_time) {
>> +			pr_debug("consecutive begin events (%s) for pid %d, vcpu %d\n",
>> +				 evsel->name, sample->pid, vcpu_record->vcpu_id);
>> +		}
>
> This is not true, the ->start_time is set in handle_begin_event() for the new alloced
> vcpu_record.
>
> If you just want to know the point where is the first event lost, you can track
> it in:
>
> static bool handle_end_event(struct perf_kvm_stat *kvm,
> 			     struct vcpu_event_record *vcpu_record,
> 			     struct event_key *key,
> 			     u64 timestamp)
> {
> 	......
>
> 	/* The begin event is not caught. */
> 	if (!time_begin)                       <======
> 		return true;
>

Ok. I'll drop the patch. I added it for a reason, but can't remember why 
at the moment.

David
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