Date: Sat, 20 Aug 2011 23:05:10 +0200 From: Fabian Keil <freebsd-listen@fabiankeil.de> To: Ashley Williams <ashley.wil@gmail.com> Cc: freebsd-current@freebsd.org Subject: Re: dtrace walltimestamp Message-ID: <20110820230510.4363cefc@fabiankeil.de> In-Reply-To: <CAHTXkP%2BX=tR44QNMOzKq1bd0HhXfHoQSzOmK_CzpzksmPnT7Yg@mail.gmail.com> References: <CAHTXkP%2BX=tR44QNMOzKq1bd0HhXfHoQSzOmK_CzpzksmPnT7Yg@mail.gmail.com>
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Ashley Williams <ashley.wil@gmail.com> wrote:
> walltimestamp and timestamp don't appear to be right in BETA-1:
>=20
>=20
> # 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=3DTSC 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=3DHPET
and dev.cpu.0.cx_lowest=3DC2:
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=3DC3:
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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