Date: Sun, 24 Jun 2012 19:59:51 +0200 From: Fabian Keil <freebsd-listen@fabiankeil.de> Cc: freebsd-current@freebsd.org Subject: Re: dtrace walltimestamp Message-ID: <20120624195951.25f3e5f5@fabiankeil.de> In-Reply-To: <20110820230510.4363cefc@fabiankeil.de> References: <CAHTXkP%2BX=tR44QNMOzKq1bd0HhXfHoQSzOmK_CzpzksmPnT7Yg@mail.gmail.com> <20110820230510.4363cefc@fabiankeil.de>
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[-- Attachment #1 --] 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=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 Copying over some code from mips seems to fix this: http://www.freebsd.org/cgi/query-pr.cgi?pr=amd64/169379 Fabian [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.19 (FreeBSD) iEYEARECAAYFAk/nVZwACgkQBYqIVf93VJ38+gCfUugCgXyuI4PtlVsodqZITO6t MYkAnRHEjbdw+DGE7D+H5jRkq9bSYCRd =3m5i -----END PGP SIGNATURE-----help
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