dtrace walltimestamp

[Fabian Keil]

Ashley Williams <ashley.wil at gmail.com> wrote:

> walltimestamp and timestamp don't appear to be right in BETA-1:
> 
> 
> # dtrace -qn 'syscall::exec*:return { printf("%Y
> %s\n",walltimestamp,curpsinfo->pr_psargs); }'
> 1970 Jan  1 10:00:00 date
> 1970 Jan  1 10:00:00 ping
> 1970 Jan  1 10:00:00 ls

I can reproduce this on amd64 with a recent HEAD, walltimestamp
is always 0, which together with the dmesg warnings seems to indicate
that it's not supported (yet).

> # dtrace -qn 'syscall::exec*:return { printf("%Y
> %s\n",timestamp,curpsinfo->pr_psargs); }'
> 1970 Jan  6 12:02:27 ping
> 1970 Jan  6 12:02:29 ls
> 1970 Jan  6 12:02:31 dtrace

Note that the timestamp value is relative to the time
the system is booted (I think), and not to midnight,
January 1, 1970.

Assuming your system has been running for a few days
and the offsets are right as well, the output seems fine.

At least on my system, timestamp offsets can only can be relied
on with either kern.timecounter.hardware=TSC or with C3
states disabled, though.

Measuring the elapsed time (in ms) between events that happen
in roughly 1 second intervals with kern.timecounter.hardware=HPET
and dev.cpu.0.cx_lowest=C2:

  elapsed
           value  ------------- Distribution ------------- count
             990 |                                         0
            1000 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@  57
            1010 |                                         0
            1020 |                                         0
            1030 |@                                        1
            1040 |                                         0

  elapsed avg                                                    1007

And doing the same with dev.cpu.0.cx_lowest=C3:

  elapsed
           value  ------------- Distribution ------------- count
              40 |                                         0
              50 |@@@@@@@@@@@@@@@@@@@                      28
              60 |@@@@@@@                                  10
              70 |@@@                                      5
              80 |@                                        1
              90 |                                         0
             100 |@                                        2
             110 |@                                        2
             120 |@                                        2
             130 |                                         0
             140 |@                                        1
             150 |@                                        1
             160 |@                                        1
             170 |@                                        1
             180 |                                         0
             190 |                                         0
             200 |                                         0
             210 |                                         0
             220 |@                                        1
             230 |@                                        1
             240 |                                         0
             250 |                                         0
             260 |                                         0
             270 |                                         0
             280 |                                         0
             290 |@                                        1
             300 |@                                        1
             310 |                                         0
             320 |@                                        1
             330 |                                         0

  elapsed avg                                                      90

Fabian
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