linux-kernel - Re: [PATCH] perf tools: intel-pt: fix endless record after being terminated

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Date:   Tue, 14 Jan 2020 15:45:56 +0200
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Jiri Olsa <jolsa@...hat.com>, Wei Li <liwei391@...wei.com>
Cc:     acme@...nel.org, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, namhyung@...nel.org,
        peterz@...radead.org, mingo@...hat.com,
        linux-kernel@...r.kernel.org, huawei.libin@...wei.com
Subject: Re: [PATCH] perf tools: intel-pt: fix endless record after being
 terminated

On 6/01/20 2:02 pm, Jiri Olsa wrote:
> On Thu, Jan 02, 2020 at 03:42:11PM +0800, Wei Li wrote:
>> In __cmd_record(), when receiving SIGINT(ctrl + c), a done flag will
>> be set and the event list will be disabled by evlist__disable() once.
>>
>> While in auxtrace_record.read_finish(), the related events will be
>> enabled again, if they are continuous, the recording seems to be endless.
>>
>> If the intel_pt event is disabled, we don't enable it again here.
>>
>> Before the patch:
>> huawei@...wei-2288H-V5:~/linux-5.5-rc4/tools/perf$ ./perf record -e \
>> intel_pt//u -p 46803
>> ^C^C^C^C^C^C
>>
>> After the patch:
>> huawei@...wei-2288H-V5:~/linux-5.5-rc4/tools/perf$ ./perf record -e \
>> intel_pt//u -p 48591
>> ^C[ perf record: Woken up 0 times to write data ]
>> Warning:
>> AUX data lost 504 times out of 4816!
>>
>> [ perf record: Captured and wrote 2024.405 MB perf.data ]
>>
>> Signed-off-by: Wei Li <liwei391@...wei.com>
>> ---
>>  tools/perf/arch/x86/util/intel-pt.c | 10 +++++++---
>>  1 file changed, 7 insertions(+), 3 deletions(-)
>>
>> diff --git a/tools/perf/arch/x86/util/intel-pt.c b/tools/perf/arch/x86/util/intel-pt.c
>> index 20df442fdf36..1e96afcd8646 100644
>> --- a/tools/perf/arch/x86/util/intel-pt.c
>> +++ b/tools/perf/arch/x86/util/intel-pt.c
>> @@ -1173,9 +1173,13 @@ static int intel_pt_read_finish(struct auxtrace_record *itr, int idx)
>>  	struct evsel *evsel;
>>  
>>  	evlist__for_each_entry(ptr->evlist, evsel) {
>> -		if (evsel->core.attr.type == ptr->intel_pt_pmu->type)
>> -			return perf_evlist__enable_event_idx(ptr->evlist, evsel,
>> -							     idx);
>> +		if (evsel->core.attr.type == ptr->intel_pt_pmu->type) {
>> +			if (evsel->disabled)
>> +				return 0;
>> +			else
>> +				return perf_evlist__enable_event_idx(
>> +						ptr->evlist, evsel, idx);
> 
> what's the logic behind enabling the event in here?

Tracing stops when the auxtrace buffer is full and won't start again until
the event is scheduled in (which is never for system-wide events) but
enabling here will start tracing again immediately if possible.