linux-kernel - Re: [PATCH v13 1/8] perf tools: Drop redundant evsel->overwrite indicator

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Date:	Wed, 6 Jul 2016 18:55:33 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	Jiri Olsa <jolsa@...hat.com>
CC:	<acme@...nel.org>, <linux-kernel@...r.kernel.org>,
	<pi3orama@....com>, <lizefan@...wei.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	He Kuang <hekuang@...wei.com>, Jiri Olsa <jolsa@...nel.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Nilay Vaish <nilayvaish@...il.com>
Subject: Re: [PATCH v13 1/8] perf tools: Drop redundant evsel->overwrite
 indicator



On 2016/7/6 18:53, Jiri Olsa wrote:
> On Mon, Jul 04, 2016 at 06:20:02AM +0000, Wang Nan wrote:
>
> SNIP
>
>> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
>> index 0fea724..3abe519 100644
>> --- a/tools/perf/util/evsel.c
>> +++ b/tools/perf/util/evsel.c
>> @@ -1359,6 +1359,9 @@ static int __perf_evsel__open(struct perf_evsel *evsel, struct cpu_map *cpus,
>>   	int pid = -1, err;
>>   	enum { NO_CHANGE, SET_TO_MAX, INCREASED_MAX } set_rlimit = NO_CHANGE;
>>   
>> +	if (perf_missing_features.write_backward && evsel->attr.write_backward)
>> +		return -EINVAL;
>> +
>>   	if (evsel->system_wide)
>>   		nthreads = 1;
>>   	else
>> @@ -1389,11 +1392,6 @@ fallback_missing_features:
>>   	if (perf_missing_features.lbr_flags)
>>   		evsel->attr.branch_sample_type &= ~(PERF_SAMPLE_BRANCH_NO_FLAGS |
>>   				     PERF_SAMPLE_BRANCH_NO_CYCLES);
>> -	if (perf_missing_features.write_backward) {
>> -		if (evsel->overwrite)
>> -			return -EINVAL;
>> -		evsel->attr.write_backward = false;
>> -	}
> so we don't change the attr.write_backward anymore?
> based on the kernel support..

We don't need fallback here. If evsel->attr.write_backward is selected
and it is missing, we should fail.

> we do it for other features, why not here? also changelog
> did not mentioned it at all ;-)
>
> thanks,
> jirka