linux-kernel - RE: [PATCH] perf sched: fix wrong conversion of task state

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Date:	Wed, 27 Jul 2016 15:58:21 +0000
From:	関山友輝 / SEKIYAMA，TOMOKI 
	<tomoki.sekiyama.qu@...achi.com>
To:	David Ahern <dsahern@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:	"ltc-kernel@...ml.intra.hitachi.co.jp" 
	<ltc-kernel@...ml.intra.hitachi.co.jp>,
	森谷真寿美 / MORITANI，MASUMI 
	<masumi.moritani.ju@...achi.com>, Jiri Olsa <jolsa@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"Masami Hiramatsu" <mhiramat@...nel.org>
Subject: RE: [PATCH] perf sched: fix wrong conversion of task state

Hi David,

Thank you for the review.

On 2016/7/27 23:18, David Ahern wrote:
> On 7/27/16 6:54 AM, Tomoki Sekiyama wrote:
>> sched_out_state() converts the prev_state u64 bitmask to a char in
>> a wrong way, which may cause wrong results of 'perf sched latency'.
>> This patch fixes the conversion.
>>
>> Signed-off-by: Tomoki Sekiyama <tomoki.sekiyama.qu@...achi.com>
>> Cc: Jiri Olsa <jolsa@...nel.org>
>> Cc: David Ahern <dsahern@...il.com>
>> Cc: Namhyung Kim <namhyung@...nel.org>
>> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
>> Cc: Masami Hiramatsu <mhiramat@...nel.org>
>> ---
>>  tools/perf/builtin-sched.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
>> index 0dfe8df..eb2f7f4 100644
>> --- a/tools/perf/builtin-sched.c
>> +++ b/tools/perf/builtin-sched.c
>> @@ -71,6 +71,7 @@ struct sched_atom {
>>  };
>>
>>  #define TASK_STATE_TO_CHAR_STR "RSDTtZXxKWP"
>> +#define TASK_STATE_MASK 0x7ff
>
>The mask should not be needed and looking at top of tree there are 2 new 
>states (N and n) that need to be added.

I couldn't find the state for 'n'. Where can I find it?
I have rechecked the code and found that __trace_sched_switch_state() uses
TASK_STATE_MAX for preempted tasks.
I will add 'N', and '+' (instead of "R+" ftrace shows) for preempted tasks.
(Also add_sched_out_event should set THREAD_WAIT_CPU for preempted tasks.)


>>
>>  enum thread_state {
>>  	THREAD_SLEEPING = 0,
>> @@ -899,7 +900,7 @@ static char sched_out_state(u64 prev_state)
>>  {
>>  	const char *str = TASK_STATE_TO_CHAR_STR;
>>
>> -	return str[prev_state];
>> +	return str[ffs(prev_state & TASK_STATE_MASK)];
>>  }
>>
>>  static int
>>
>
> Handle unknown bits with '?' like the kernel does (see task_state_char 
> and sched_show_task).

OK, I will make it return '?' for unknown states.

Will update the patch soon.

Thanks,
Tomoki Sekiyama