[PATCH v2] perf sched: fix wrong conversion of task state

[PATCH v2] perf sched: fix wrong conversion of task state

[Tomoki Sekiyama]

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.
Also, preempted tasks must be considered that they are in the
THREAD_WAIT_CPU state.

Signed-off-by: Tomoki Sekiyama <tomoki.sekiyama.qu@hitachi.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
---
 tools/perf/builtin-sched.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
index 0dfe8df..8651c36 100644
--- a/tools/perf/builtin-sched.c
+++ b/tools/perf/builtin-sched.c
@@ -70,7 +70,8 @@ struct sched_atom {
 	struct task_desc	*wakee;
 };
 
-#define TASK_STATE_TO_CHAR_STR "RSDTtZXxKWP"
+/* TASK_STATE_MAX means the task is preempted(R+). Use '+' for it here. */
+#define TASK_STATE_TO_CHAR_STR "RSDTtXZxKWPN+"
 
 enum thread_state {
 	THREAD_SLEEPING = 0,
@@ -897,9 +898,10 @@ static int thread_atoms_insert(struct perf_sched *sched, struct thread *thread)
 
 static char sched_out_state(u64 prev_state)
 {
-	const char *str = TASK_STATE_TO_CHAR_STR;
+	const char str[] = TASK_STATE_TO_CHAR_STR;
+	unsigned int bit = prev_state ? __ffs(prev_state) + 1 : 0;
 
-	return str[prev_state];
+	return bit < sizeof(str) - 1 ? str[bit] : '?';
 }
 
 static int
@@ -915,7 +917,7 @@ add_sched_out_event(struct work_atoms *atoms,
 
 	atom->sched_out_time = timestamp;
 
-	if (run_state == 'R') {
+	if (run_state == 'R' || run_state == '+') {
 		atom->state = THREAD_WAIT_CPU;
 		atom->wake_up_time = atom->sched_out_time;
 	}
-- 
2.7.4

Re: [PATCH v2] perf sched: fix wrong conversion of task state

[David Ahern]

On 7/27/16 10:07 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.
> Also, preempted tasks must be considered that they are in the
> THREAD_WAIT_CPU state.

you reference fixing the order of XZ as well.

>
> Signed-off-by: Tomoki Sekiyama <tomoki.sekiyama.qu@hitachi.com>
> Cc: Jiri Olsa <jolsa@kernel.org>
> Cc: David Ahern <dsahern@gmail.com>
> Cc: Namhyung Kim <namhyung@kernel.org>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Cc: Masami Hiramatsu <mhiramat@kernel.org>
> ---
>  tools/perf/builtin-sched.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
> index 0dfe8df..8651c36 100644
> --- a/tools/perf/builtin-sched.c
> +++ b/tools/perf/builtin-sched.c
> @@ -70,7 +70,8 @@ struct sched_atom {
>  	struct task_desc	*wakee;
>  };
>
> -#define TASK_STATE_TO_CHAR_STR "RSDTtZXxKWP"
> +/* TASK_STATE_MAX means the task is preempted(R+). Use '+' for it here. */
> +#define TASK_STATE_TO_CHAR_STR "RSDTtXZxKWPN+"

As I mentioned in a previous reply you can't add the '+' on the end.

Re: [PATCH v2] perf sched: fix wrong conversion of task state

[Masami Hiramatsu]

On Thu, 28 Jul 2016 01:07:40 +0900
Tomoki Sekiyama <tomoki.sekiyama.qu@hitachi.com> 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.
> Also, preempted tasks must be considered that they are in the
> THREAD_WAIT_CPU state.

Hmm, this includes several fixes and enhancements.
1. Use first bit of the state instead of state itself (critical bug to avoid crash?)
2. Check the range of the array and return '?' if out (minor bug, it can access data area)
3. Fix TASK_STATE_TO_CHAR_STR to swap X and Z.
4. Add new 'N+' to TASK_STATE_TO_CHAR_STR. (how about 'n'?)
5. Treat a preempted task as THREAD_WAIT_CPU.

so IMHO, it is better to split this patch into atleast 2, #1 and #2 (critical bugfix),
#3, #4, and #5 (minor update).

[..]
> @@ -897,9 +898,10 @@ static int thread_atoms_insert(struct perf_sched *sched, struct thread *thread)
>  
>  static char sched_out_state(u64 prev_state)
>  {
> -	const char *str = TASK_STATE_TO_CHAR_STR;
> +	const char str[] = TASK_STATE_TO_CHAR_STR;
> +	unsigned int bit = prev_state ? __ffs(prev_state) + 1 : 0;
>  
> -	return str[prev_state];
> +	return bit < sizeof(str) - 1 ? str[bit] : '?';

You'd better use ARRAY_SIZE(str) instead of sizeof() for array here.

Thank you,


-- 
Masami Hiramatsu <mhiramat@kernel.org>

RE: [PATCH v2] perf sched: fix wrong conversion of task state

[Tomoki Sekiyama]

Hi Hiramatsu-san,

On 2016/7/28, 2016 8:43, Masami Hiramatsu wrote:
> Hmm, this includes several fixes and enhancements.
> 1. Use first bit of the state instead of state itself (critical bug to
avoid crash?)
> 2. Check the range of the array and return '?' if out (minor bug, it can
access data area)
> 3. Fix TASK_STATE_TO_CHAR_STR to swap X and Z.
> 4. Add new 'N+' to TASK_STATE_TO_CHAR_STR. (how about 'n'?)
> 5. Treat a preempted task as THREAD_WAIT_CPU.
>
> so IMHO, it is better to split this patch into atleast 2, #1 and #2
(critical bugfix),
> #3, #4, and #5 (minor update).

This time I will fix only the invalid array access and
adapting to the current kernel TASK_STATE, and leave the
preempted task handling for later follow-up.

 [..]
>> @@ -897,9 +898,10 @@ static int thread_atoms_insert(struct perf_sched
*sched, struct thread *thread)
>> +	return bit < sizeof(str) - 1 ? str[bit] : '?';
>
> You'd better use ARRAY_SIZE(str) instead of sizeof() for array here.

OK, will change this to use ARRAY_SIZE on the next update.

Thanks,
Tomoki Sekiyama