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

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Date:	Wed, 27 Jul 2016 08:18:14 -0600
From:	David Ahern <dsahern@...il.com>
To:	Tomoki Sekiyama <tomoki.sekiyama.qu@...achi.com>,
	linux-kernel@...r.kernel.org
Cc:	ltc-kernel@...ml.intra.hitachi.co.jp,
	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

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.

>
>  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).