Date: Wed, 6 May 2009 20:13:02 +1000 From: Peter Jeremy <peterjeremy@optushome.com.au> To: freebsd-current@freebsd.org Subject: hardclock() sources Message-ID: <20090506101301.GA17874@server.vk2pj.dyndns.org>
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--ZPt4rx8FFjLCG7dd Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Currently, FreeBSD uses the LAPIC timer to derive both hardclock() and statclock()/profclock() if it exists, otherwise it uses the 8254 and RTC. This presents a problem for using C3 - which stops the LAPIC clock. Some time ago, ariff@ produced a patch to work around a similar problem with C1E on some AMD Turion CPUs: http://people.freebsd.org/~ariff/misc/idlecpu_apic_5.diff A better solution would seem to be to use a HPET periodic timer. Is there a particular reason why code to (at least optionally) support HPET as the timer interrupt hasn't been written? Looking back through the archives, pkh@ has made disparaging remarks about the actual usefulness of HPET (as against the Intel documentation) but I can't find anything that actually talks about using it. Note that supporting HPET as a timer source would provide at least some of the infrastructure that will be needed for a future tickless kernel. --=20 Peter Jeremy --ZPt4rx8FFjLCG7dd Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.11 (FreeBSD) iEYEARECAAYFAkoBYq0ACgkQ/opHv/APuIfLngCfbgRt+478eQO1CaAtCPltykir W2gAoI8Tga5coWvjU5X8wR7wDoRhy9x6 =rfRx -----END PGP SIGNATURE----- --ZPt4rx8FFjLCG7dd--
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