[dtrace-discuss] sched provider - what do on-cpu & off-cpu signify?

[Alexander Kolbasov]

Tim,

you are observing the idle thread. Try adding

sched:::on-cpu
/(uintptr_t)curthread->t_startpc != (uintptr_t)`idle/

- akolb

> *,
> 
> So, I was reading the definition of sched:::on-cpu and sched:::off-cpu
> to mean that any thread dispatched on a CPU would have that activity
> bounded by on-cpu and off-cpu firings, and that the use of "timestamp"
> between these points would accurately show how much CPU the thread was
> using.
> 
> My prototype script gets a little over 90% on a nearly idle system, though (this 
> system has 2 CPUs, BTW):
> 
> $ cat on-off.d
> #!/usr/sbin/dtrace -s
> 
> #pragma D option quiet
> 
> int64_t start_bolt;
> uint64_t start_n;
> int64_t util;
> 
> BEGIN
> {
>          start_bolt = `lbolt64;
>          start_n = timestamp;
>          util = 0;
> }
> 
> sched:::on-cpu
> {
>          self->on_n = timestamp;
> }
> 
> 
> sched:::off-cpu
> /self->on_n/
> {
>          util += timestamp - self->on_n;
>          self->on_n = 0;
> }
> 
> profile:::tick-5s
> {
>          printf("elapsed (ticks): %ld\n", `lbolt64 - start_bolt);
>          printf("elapsed (ns)   : %lu\n", timestamp - start_n);
>          printf("util (ns)      : %ld\n", util);
>          start_bolt = `lbolt64;
>          start_n = timestamp;
>          util = 0;
> }
> 
> 
> 
> mashie[bash]# ./on-off.d
> elapsed (ticks): 498
> elapsed (ns)   : 4979669863
> util (ns)      : 9137442436
> elapsed (ticks): 500
> elapsed (ns)   : 5000000822
> util (ns)      : 9185407490
> elapsed (ticks): 500
> elapsed (ns)   : 4999999221
> util (ns)      : 9157844649
> 
> 
> mashie[bash]# vmstat 5 4		(run at the same time)
> mashie ) vmstat 5 4
>   kthr      memory            page            disk          faults      cpu
>   r b w   swap  free  re  mf pi po fr de sr s0 s1 -- --   in   sy   cs us sy id
>   0 0 0 815384 906900  2  16  7  1  1  0  6  1 -5  0  0  646 1605  816  6  4 90
>   0 0 0 625700 706632  0   6  0  0  0  0  0  0  0  0  0  848  880  628  2  2 97
>   0 0 0 625700 706632  0   0  0  0  0  0  0  0  0  0  0  850  909  659  2  2 96
>   0 0 0 625700 706632  0   0  0  0  0  0  0  0  0  0  0  869 1297  823  2  2 96
> 
> 
> Does on-cpu, off-cpu also pick up when threads are in idle()?  If so, what is 
> the best way to exclude that (just put clauses on fbt::idle)?