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

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Date:	Mon, 05 Aug 2013 14:53:30 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	David Ahern <dsahern@...il.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 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.

> 
> 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;

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