linux-kernel - Re: [PATCH] perf annotate: Remove hist__account

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Date:   Fri, 15 Mar 2019 12:20:27 +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] perf annotate: Remove hist__account_cycles from callback



On 3/14/2019 10:17 PM, Jin, Yao wrote:
> 
> 
> On 3/14/2019 8:04 PM, Jiri Olsa wrote:
>> On Wed, Mar 13, 2019 at 04:22:54AM +0800, Jin Yao wrote:
>>> The hist__account_cycles is executed when the hist_iter__branch_callback
>>> is called. But it looks it's not necessary. In hist__account_cycles, it
>>> already walks on all branch entries.
>>>
>>> This patch moves the hist__account_cycles out of callback, now the data
>>> processing is much faster than before.
>>>
>>> For example,
>>> perf record -b ...
>>> perf annotate
>>>
>>> The before/after output should be no change.
>>
>> so in the old code it was called multiple times per sample,
>> while after your change it's called just once per sample
>>
>> it increases cycles stats for symbol, so it's strange
>> the behaviour is the same.. could you please exaplin this
>> in more detail?
>>
> 
> In __symbol__account_cycles,
> ch[offset].num_aggr++;
> ch[offset].cycles_aggr += cycles;
> 
> In annotation__compute_ipc,
> al = notes->offsets[offset];
> al->cycles = ch->cycles_aggr / ch->num_aggr;
> 
> So the num_aggr and cycles_aggr are both increased n times, then the 
> final result is the same.
> 

There might be another potential issue in annotation__count_and_fill.

/* Hide data when there are too many overlaps. */
if (ch->reset >= 0x7fff || ch->reset >= ch->num / 2)
	return;

When ch->reset is 0 and ch->num is 1, it returns directly. But for this 
case, the data doesn't need to be hidden since there is no overlap 
happening.

I will post v2 and add this fix.

Thanks
Jin Yao

>>>
>>> Signed-off-by: Jin Yao <yao.jin@...ux.intel.com>
>>> ---
>>>   tools/perf/builtin-annotate.c | 4 ++--
>>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/tools/perf/builtin-annotate.c 
>>> b/tools/perf/builtin-annotate.c
>>> index 67f9d9f..77deb3a 100644
>>> --- a/tools/perf/builtin-annotate.c
>>> +++ b/tools/perf/builtin-annotate.c
>>> @@ -159,8 +159,6 @@ static int hist_iter__branch_callback(struct 
>>> hist_entry_iter *iter,
>>>       struct perf_evsel *evsel = iter->evsel;
>>>       int err;
>>> -    hist__account_cycles(sample->branch_stack, al, sample, false);
>>> -
>>
>> there's similar code in perf report, could you please cover
>> that as well?
>>
> 
> Sure, let me have a try.
> 
> Thanks
> Jin Yao
> 
>> thanks,
>> jirka
>>
>>>       bi = he->branch_info;
>>>       err = addr_map_symbol__inc_samples(&bi->from, sample, evsel);
>>> @@ -199,6 +197,8 @@ static int process_branch_callback(struct 
>>> perf_evsel *evsel,
>>>       if (a.map != NULL)
>>>           a.map->dso->hit = 1;
>>> +    hist__account_cycles(sample->branch_stack, al, sample, false);
>>> +
>>>       ret = hist_entry_iter__add(&iter, &a, PERF_MAX_STACK_DEPTH, ann);
>>>       return ret;
>>>   }
>>> -- 
>>> 2.7.4
>>>