linux-kernel - Re: [PATCH 25/28] perf top: Convert to hist_entry

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Date:	Mon, 13 Jan 2014 17:55:46 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Arun Sharma <asharma@...com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Rodrigo Campos <rodrigo@...g.com.ar>
Subject: Re: [PATCH 25/28] perf top: Convert to hist_entry_iter

On Sat, 11 Jan 2014 17:35:29 +0100, Jiri Olsa wrote:
> On Wed, Jan 08, 2014 at 05:46:30PM +0900, Namhyung Kim wrote:
>> Reuse hist_entry_iter__add() function to share the similar code with
>> perf report.  Note that it needs to be called with hists.lock so tweak
>> some internal functions not to deadlock or hold the lock too long.
>> 
>> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
>> ---
>>  tools/perf/builtin-top.c | 75 ++++++++++++++++++++++++------------------------
>>  1 file changed, 37 insertions(+), 38 deletions(-)
>> 
>> diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
>> index f0f55e6030cd..cf330c66bed7 100644
>> --- a/tools/perf/builtin-top.c
>> +++ b/tools/perf/builtin-top.c
>> @@ -186,9 +186,6 @@ static void perf_top__record_precise_ip(struct perf_top *top,
>>  	sym = he->ms.sym;
>>  	notes = symbol__annotation(sym);
>>  
>> -	if (pthread_mutex_trylock(&notes->lock))
>> -		return;
>> -
>>  	ip = he->ms.map->map_ip(he->ms.map, ip);
>>  	err = hist_entry__inc_addr_samples(he, counter, ip);
>>  
>> @@ -201,6 +198,8 @@ static void perf_top__record_precise_ip(struct perf_top *top,
>>  		       sym->name);
>>  		sleep(1);
>>  	}
>> +
>> +	pthread_mutex_lock(&notes->lock);
>>  }
>
> locking on function exit.. does not look right ;-)

Yes, it looks weird.. but it's because of the change in locking.  After
I changed perf top to use the hist_entry_iter, it needed to protect
the whole hist_entry_iter__add() by hists->lock so the
perf_top__record_precise_ip() should be called with the lock acquired.

I might remove the lock in the function completely, but it seemed not
good since it goes to sleep with the lock then.  So I added the
(reverse) unlock/lock dance to avoid it.

So yes, I think I need to add a comment to explain this. :)

Thanks,
Namhyung
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