linux-kernel - Re: [PATCH v2 1/3] perf report: Change sort order by a specified event in group

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Date:   Wed, 11 Dec 2019 20:36:26 +0800
From:   "Jin, Yao" <yao.jin@...ux.intel.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     acme@...nel.org, jolsa@...nel.org, peterz@...radead.org,
        mingo@...hat.com, alexander.shishkin@...ux.intel.com,
        Linux-kernel@...r.kernel.org, ak@...ux.intel.com,
        kan.liang@...el.com, yao.jin@...el.com
Subject: Re: [PATCH v2 1/3] perf report: Change sort order by a specified
 event in group



On 12/11/2019 8:14 PM, Jiri Olsa wrote:
> On Wed, Dec 11, 2019 at 08:01:44PM +0800, Jin, Yao wrote:
>>
>>
>> On 12/11/2019 7:38 PM, Jiri Olsa wrote:
>>> On Wed, Dec 11, 2019 at 03:30:34PM +0800, Jin Yao wrote:
>>>
>>> SNIP
>>>
>>>> +
>>>> +static int __hpp__group_sort_idx(struct hist_entry *a, struct hist_entry *b,
>>>> +				 hpp_field_fn get_field, int idx)
>>>> +{
>>>> +	struct evsel *evsel = hists_to_evsel(a->hists);
>>>> +	u64 *fields_a, *fields_b;
>>>> +	int cmp, nr_members, ret, i;
>>>> +
>>>> +	cmp = field_cmp(get_field(a), get_field(b));
>>>> +	if (!perf_evsel__is_group_event(evsel))
>>>> +		return cmp;
>>>> +
>>>> +	nr_members = evsel->core.nr_members;
>>>> +	ret = pair_fields_alloc(a, b, get_field, nr_members,
>>>> +			      &fields_a, &fields_b);
>>>> +	if (ret) {
>>>> +		ret = cmp;
>>>> +		goto out;
>>>> +	}
>>>> +
>>>> +	for (i = 1; i < nr_members; i++) {
>>>> +		if (i == idx) {
>>>> +			ret = field_cmp(fields_a[i], fields_b[i]);
>>>> +			if (ret)
>>>> +				goto out;
>>>> +		}
>>>> +	}
>>>> +
>>>> +	if (cmp) {
>>>> +		ret = cmp;
>>>> +		goto out;
>>>> +	}
>>>> +
>>>> +	for (i = 1; i < nr_members; i++) {
>>>> +		if (i != idx) {
>>>> +			ret = field_cmp(fields_a[i], fields_b[i]);
>>>> +			if (ret)
>>>> +				goto out;
>>>> +		}
>>>
>>> hi,
>>> I'm missing why we compare the fields for 2nd time in here
>>>
>>> thanks,
>>> jirka
>>>
>>
>> Hi,
>>
>> I think we may continue comparing the remaining of fields if the index field
>> is equal. :)
> 
> aah, I missed it's actualy == used in the first one ;-)
> 
> why don't you just call it directly?
> 
> 	ret = field_cmp(fields_a[idx], fields_b[idx])
> 	if (ret)
> 		goto out;
> 
> jirka
> 

Oh, yes, we can use simpler code. For example,

	if (idx >= 1 && idx < nr_members) {
		ret = field_cmp(fields_a[idx], fields_b[idx]);
		if (ret)
			goto out;
	}

Thanks
Jin Yao