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Fabian Keil <freebsd-listen@fabiankeil.de> wrote:
> 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.
>=20
> 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:
>=20
> elapsed
> value ------------- Distribution ------------- count
> 990 | 0
> 1000 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 57
> 1010 | 0
> 1020 | 0
> 1030 |@ 1
> 1040 | 0
>=20
> elapsed avg 1007
>=20
> And doing the same with dev.cpu.0.cx_lowest=3DC3:
>=20
> 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
>=20
> elapsed avg 90
Copying over some code from mips seems to fix this:
http://www.freebsd.org/cgi/query-pr.cgi?pr=3Damd64/169379
Fabian
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