What is _prev_state in sched_switch?

What is _prev_state in sched_switch?

[Ravindra Kumar Meena]

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Hi,

I had a looked at TraceCompass example. I came across sched_swithc event in
present in the metadata.

event {
name = "sched_switch";
id = 27;
stream_id = 0;
fields := struct {
integer { size = 8; align = 8; signed = 0; encoding = UTF8; base = 10; }
_prev_comm[16];
integer { size = 32; align = 8; signed = 1; encoding = none; base = 10; }
_prev_tid;
integer { size = 32; align = 8; signed = 1; encoding = none; base = 10; }
_prev_prio;
integer { size = 64; align = 8; signed = 1; encoding = none; base = 10; }
_prev_state;
integer { size = 8; align = 8; signed = 0; encoding = UTF8; base = 10; }
_next_comm[16];
integer { size = 32; align = 8; signed = 1; encoding = none; base = 10; }
_next_tid;
integer { size = 32; align = 8; signed = 1; encoding = none; base = 10; }
_next_prio;
};
};

All event.fields variables are clear to me but what does _prev_state do
here? I had a looked at its babeltrace output but found no pattern in
_prev_state value.

Please attend this email ASAP.

Thanks

-- 
*Ravindra Kumar Meena*,
B. Tech. Computer Science and Engineering,
Indian Institute of Technology (Indian School of Mines)
<https://www.iitism.ac.in/>, Dhanbad

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Re: What is _prev_state in sched_switch?

[Sebastien Boisvert]

On 2019-07-24 2:44 a.m., Ravindra Kumar Meena wrote:
> Hi,
> 
> I had a looked at TraceCompass example. I came across sched_swithc event in present in the metadata.
> 
> event {
> name = "sched_switch";
> id = 27;
> stream_id = 0;
> fields := struct {
> integer { size = 8; align = 8; signed = 0; encoding = UTF8; base = 10; } _prev_comm[16];
> integer { size = 32; align = 8; signed = 1; encoding = none; base = 10; } _prev_tid;
> integer { size = 32; align = 8; signed = 1; encoding = none; base = 10; } _prev_prio;
> integer { size = 64; align = 8; signed = 1; encoding = none; base = 10; } _prev_state;
> integer { size = 8; align = 8; signed = 0; encoding = UTF8; base = 10; } _next_comm[16];
> integer { size = 32; align = 8; signed = 1; encoding = none; base = 10; } _next_tid;
> integer { size = 32; align = 8; signed = 1; encoding = none; base = 10; } _next_prio;
> };
> };
> 
> All event.fields variables are clear to me but what does _prev_state do here? I had a looked at its babeltrace output but found no pattern in _prev_state value.
> 
> Please attend this email ASAP.

I think that writing "Please attend this email ASAP" is somehow rude.

> 
> Thanks
> 
> -- 
> *Ravindra Kumar Meena*,
> B. Tech. Computer Science and Engineering,
> Indian Institute of Technology (Indian School of Mines) <https://www.iitism.ac.in/>, Dhanbad
> 
> _______________________________________________
> lttng-dev mailing list
> lttng-dev@lists.lttng.org
> https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
> 

Re: What is _prev_state in sched_switch?

[Ravindra Kumar Meena]

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On Wed, Jul 24, 2019, 7:33 PM Sebastien Boisvert <sboisvert@gydle.com>
wrote:

>
>
> On 2019-07-24 2:44 a.m., Ravindra Kumar Meena wrote:
> > Hi,
> >
> > I had a looked at TraceCompass example. I came across sched_swithc event
> in present in the metadata.
> >
> > event {
> > name = "sched_switch";
> > id = 27;
> > stream_id = 0;
> > fields := struct {
> > integer { size = 8; align = 8; signed = 0; encoding = UTF8; base = 10; }
> _prev_comm[16];
> > integer { size = 32; align = 8; signed = 1; encoding = none; base = 10;
> } _prev_tid;
> > integer { size = 32; align = 8; signed = 1; encoding = none; base = 10;
> } _prev_prio;
> > integer { size = 64; align = 8; signed = 1; encoding = none; base = 10;
> } _prev_state;
> > integer { size = 8; align = 8; signed = 0; encoding = UTF8; base = 10; }
> _next_comm[16];
> > integer { size = 32; align = 8; signed = 1; encoding = none; base = 10;
> } _next_tid;
> > integer { size = 32; align = 8; signed = 1; encoding = none; base = 10;
> } _next_prio;
> > };
> > };
> >
> > All event.fields variables are clear to me but what does _prev_state do
> here? I had a looked at its babeltrace output but found no pattern in
> _prev_state value.
> >
> > Please attend this email ASAP.
>
> I think that writing "Please attend this email ASAP" is somehow rude.
>
Okay. Sorry for that. It won't happen again.

I want to know what _prev_state means in sched_switch event.

>

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Re: What is _prev_state in sched_switch?

[Sebastien Boisvert]

Hello Ravindra,

On 2019-07-24 10:09 a.m., Ravindra Kumar Meena wrote:
> 
> 
> On Wed, Jul 24, 2019, 7:33 PM Sebastien Boisvert <sboisvert@gydle.com <mailto:sboisvert@gydle.com>> wrote:
> 
> 
> 
>     On 2019-07-24 2:44 a.m., Ravindra Kumar Meena wrote:
>     > Hi,
>     >
>     > I had a looked at TraceCompass example. I came across sched_swithc event in present in the metadata.
>     >
>     > event {
>     > name = "sched_switch";
>     > id = 27;
>     > stream_id = 0;
>     > fields := struct {
>     > integer { size = 8; align = 8; signed = 0; encoding = UTF8; base = 10; } _prev_comm[16];
>     > integer { size = 32; align = 8; signed = 1; encoding = none; base = 10; } _prev_tid;
>     > integer { size = 32; align = 8; signed = 1; encoding = none; base = 10; } _prev_prio;
>     > integer { size = 64; align = 8; signed = 1; encoding = none; base = 10; } _prev_state;
>     > integer { size = 8; align = 8; signed = 0; encoding = UTF8; base = 10; } _next_comm[16];
>     > integer { size = 32; align = 8; signed = 1; encoding = none; base = 10; } _next_tid;
>     > integer { size = 32; align = 8; signed = 1; encoding = none; base = 10; } _next_prio;
>     > };
>     > };
>     >
>     > All event.fields variables are clear to me but what does _prev_state do here? I had a looked at its babeltrace output but found no pattern in _prev_state value.
>     >
>     > Please attend this email ASAP.
> 
>     I think that writing "Please attend this email ASAP" is somehow rude.
> 
> Okay. Sorry for that. It won't happen again.
> 
> I want to know what _prev_state means in sched_switch event.
> 

In the Linux kernel, the tracepoint for sched_switch does not have the
field prev_state:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/tracepoint.h?id=52a6e82ac27288f591c750f201de5c3e6ef24385#n465


In lttng-modules, however, there is the field prev_state:

http://git.lttng.org/?p=lttng-modules.git;a=blob;f=instrumentation/events/lttng-module/sched.h;h=77d77b2aeeddbe6ac34e2228b077734721f45b18;hb=4ea9b7c98ade603b08f0d945f4d99bc079eb57b6#l237


My guess would be that prev_state is the previous state of the thread (TID):

in "man ps":

PROCESS STATE CODES
       Here are the different values that the s, stat and state output specifiers (header "STAT" or "S") will display to describe the state of a process:

               D    uninterruptible sleep (usually IO)
               R    running or runnable (on run queue)
               S    interruptible sleep (waiting for an event to complete)
               T    stopped by job control signal
               t    stopped by debugger during the tracing
               W    paging (not valid since the 2.6.xx kernel)
               X    dead (should never be seen)
               Z    defunct ("zombie") process, terminated but not reaped by its parent


In the Linux kernel:

$ grep "#define TASK_" include/linux/sched.h
#define TASK_RUNNING			0x0000
#define TASK_INTERRUPTIBLE		0x0001
#define TASK_UNINTERRUPTIBLE		0x0002
#define TASK_PARKED			0x0040
#define TASK_DEAD			0x0080
#define TASK_WAKEKILL			0x0100
#define TASK_WAKING			0x0200
#define TASK_NOLOAD			0x0400
#define TASK_NEW			0x0800
#define TASK_STATE_MAX			0x1000
#define TASK_KILLABLE			(TASK_WAKEKILL | TASK_UNINTERRUPTIBLE)
#define TASK_STOPPED			(TASK_WAKEKILL | __TASK_STOPPED)
#define TASK_TRACED			(TASK_WAKEKILL | __TASK_TRACED)
#define TASK_IDLE			(TASK_UNINTERRUPTIBLE | TASK_NOLOAD)
#define TASK_NORMAL			(TASK_INTERRUPTIBLE | TASK_UNINTERRUPTIBLE)
#define TASK_REPORT			(TASK_RUNNING | TASK_INTERRUPTIBLE | \


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Re: What is _prev_state in sched_switch?

[Ravindra Kumar Meena]

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>
> >     On 2019-07-24 2:44 a.m., Ravindra Kumar Meena wrote:
> >     > Hi,
> >     >
> >     > I had a looked at TraceCompass example. I came across sched_swithc
> event in present in the metadata.
> >     >
> >     > event {
> >     > name = "sched_switch";
> >     > id = 27;
> >     > stream_id = 0;
> >     > fields := struct {
> >     > integer { size = 8; align = 8; signed = 0; encoding = UTF8; base =
> 10; } _prev_comm[16];
> >     > integer { size = 32; align = 8; signed = 1; encoding = none; base
> = 10; } _prev_tid;
> >     > integer { size = 32; align = 8; signed = 1; encoding = none; base
> = 10; } _prev_prio;
> >     > integer { size = 64; align = 8; signed = 1; encoding = none; base
> = 10; } _prev_state;
> >     > integer { size = 8; align = 8; signed = 0; encoding = UTF8; base =
> 10; } _next_comm[16];
> >     > integer { size = 32; align = 8; signed = 1; encoding = none; base
> = 10; } _next_tid;
> >     > integer { size = 32; align = 8; signed = 1; encoding = none; base
> = 10; } _next_prio;
> >     > };
> >     > };
> >     >
> >     > All event.fields variables are clear to me but what does
> _prev_state do here? I had a looked at its babeltrace output but found no
> pattern in _prev_state value.
>
> In the Linux kernel, the tracepoint for sched_switch does not have the
> field prev_state:
>
>
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/tracepoint.h?id=52a6e82ac27288f591c750f201de5c3e6ef24385#n465
>
>
> In lttng-modules, however, there is the field prev_state:
>
>
> http://git.lttng.org/?p=lttng-modules.git;a=blob;f=instrumentation/events/lttng-module/sched.h;h=77d77b2aeeddbe6ac34e2228b077734721f45b18;hb=4ea9b7c98ade603b08f0d945f4d99bc079eb57b6#l237
>
>
> My guess would be that prev_state is the previous state of the thread
> (TID):
>
Okay. The above link was somewhat helpful but I still didn't get what is
the meaning of {0, 1, 1026, 4096} values in _prev_state.

In babeltrace output _prev_state have { 0, 1, 1026, 4096 } values.

The example can be found here
https://github.com/tuxology/tracevizlab/blob/master/labs/TraceCompassTutorialTraces.tgz

At folder "102-tracing-wget-critical-path/wget-first-call" babeltrace gives
following output.

babeltrace . | grep sched_switch

[21:20:44.207247650] (+0.000000799) arnaud-desktop sched_switch: { cpu_id =
3 }, { prev_comm = "swapper/3", prev_tid = 0, prev_prio = 20, prev_state =
0, next_comm = "kworker/u8:2", next_tid = 8363, next_prio = 20 }
[21:20:44.207252919] (+0.000000085) arnaud-desktop sched_switch: { cpu_id =
3 }, { prev_comm = "kworker/u8:2", prev_tid = 8363, prev_prio = 20,
prev_state = 1026, next_comm = "swapper/3", next_tid = 0, next_prio = 20 }
[21:20:44.207253370] (+0.000000143) arnaud-desktop sched_switch: { cpu_id =
0 }, { prev_comm = "code", prev_tid = 3876, prev_prio = 20, prev_state = 0,
next_comm = "code", next_tid = 4140, next_prio = 20 }
[21:20:44.207257279] (+0.000000656) arnaud-desktop sched_switch: { cpu_id =
3 }, { prev_comm = "swapper/3", prev_tid = 0, prev_prio = 20, prev_state =
0, next_comm = "kworker/u8:2", next_tid = 8363, next_prio = 20 }
[21:20:44.207258485] (+0.000000903) arnaud-desktop sched_switch: { cpu_id =
3 }, { prev_comm = "kworker/u8:2", prev_tid = 8363, prev_prio = 20,
prev_state = 1026, next_comm = "swapper/3", next_tid = 0, next_prio = 20 }
[21:20:44.207270164] (+0.000000081) arnaud-desktop sched_switch: { cpu_id =
3 }, { prev_comm = "swapper/3", prev_tid = 0, prev_prio = 20, prev_state =
0, next_comm = "kworker/u8:2", next_tid = 8363, next_prio = 20 }

P.S: This is not a full babeltrace output.


-- 
*Ravindra Kumar Meena*,
B. Tech. Computer Science and Engineering,
Indian Institute of Technology (Indian School of Mines)
<https://www.iitism.ac.in/>, Dhanbad

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Re: What is _prev_state in sched_switch?

[Christophe Bédard]

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Hi,

Re-sending since I previously used an email address not subscribed to the
ML.

On Mon, 29 Jul 2019 at 11:08, Ravindra Kumar Meena <rmeena840@gmail.com>
wrote:

> Okay. The above link was somewhat helpful but I still didn't get what is
> the meaning of {0, 1, 1026, 4096} values in _prev_state.
>
> In babeltrace output _prev_state have { 0, 1, 1026, 4096 } values.
>
>
I think the answer to your question was in Sebastien's email.

$ grep "#define TASK_" include/linux/sched.h
> #define TASK_RUNNING                    0x0000
> #define TASK_INTERRUPTIBLE              0x0001
> #define TASK_UNINTERRUPTIBLE            0x0002
> #define TASK_PARKED                     0x0040
> #define TASK_DEAD                       0x0080
> #define TASK_WAKEKILL                   0x0100
> #define TASK_WAKING                     0x0200
> #define TASK_NOLOAD                     0x0400
> #define TASK_NEW                        0x0800
> #define TASK_STATE_MAX                  0x1000
> #define TASK_KILLABLE                   (TASK_WAKEKILL |
> TASK_UNINTERRUPTIBLE)
> #define TASK_STOPPED                    (TASK_WAKEKILL | __TASK_STOPPED)
> #define TASK_TRACED                     (TASK_WAKEKILL | __TASK_TRACED)
> #define TASK_IDLE                       (TASK_UNINTERRUPTIBLE |
> TASK_NOLOAD)
> #define TASK_NORMAL                     (TASK_INTERRUPTIBLE |
> TASK_UNINTERRUPTIBLE)
> #define TASK_REPORT                     (TASK_RUNNING | TASK_INTERRUPTIBLE
> | \
>

States can be combined (OR'd).

1026 in decimal is 0x402 which is 0x400 | 0x002. That is TASK_NOLOAD |
TASK_UNINTERRUPTIBLE, or, as defined above, it's simply TASK_IDLE.

I'm not sure what other answer you're expecting.


Christophe

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Re: What is _prev_state in sched_switch?

[Sebastien Boisvert]

On 2019-07-29 5:07 a.m., Ravindra Kumar Meena wrote:
> Okay. The above link was somewhat helpful but I still didn't get what is the meaning of {0, 1, 1026, 4096} values in _prev_state. 
> 

Christophe explained, the values of _prev_state.

In addition, I suggest you read those links (from general to specific):

- https://en.wikipedia.org/wiki/Finite-state_machine
- https://en.wikipedia.org/wiki/Scheduling_(computing)
- https://www.kernel.org/doc/Documentation/scheduler/sched-design-CFS.txt
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Re: What is _prev_state in sched_switch?

[Ravindra Kumar Meena]

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>
> Christophe explained, the values of _prev_state.
>
> In addition, I suggest you read those links (from general to specific):
>
> - https://en.wikipedia.org/wiki/Finite-state_machine
> - https://en.wikipedia.org/wiki/Scheduling_(computing)
> - https://www.kernel.org/doc/Documentation/scheduler/sched-design-CFS.txt


Thanks, Christophe and Sebastien for helping me out. This resolved
the problem.


-- 
*Ravindra Kumar Meena*,
B. Tech. Computer Science and Engineering,
Indian Institute of Technology (Indian School of Mines)
<https://www.iitism.ac.in/>, Dhanbad

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