Date: Sun, 21 Dec 2008 23:32:44 +0100 From: Ivan Voras <ivoras@freebsd.org> To: freebsd-questions@freebsd.org Subject: Re: Status of hyperthreading in FreeBSD Message-ID: <gimg6d$5id$1@ger.gmane.org> In-Reply-To: <200812202039.NAA10290@lariat.net> References: <200812202039.NAA10290@lariat.net>
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This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig8F241890DBD490D25AC8994B Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Brett Glass wrote: > Which raises a question: What's the status of FreeBSD's support for > hyperthreading? As far as I know, after it was revealed that some > processes on a machine with hyperthreading could "spy" on others, and Yes, but that is a hardware problem which is independent of the operating system (it's present in all of them). > also that hyperthreading didn't always improve performance on high end > processors, the feature was turned off by default. But on single-user Yes, especially on the early Pentium 4 CPUs. This is also OS-independent.= > machines, or on servers where the CPU was likely to be shared by two > processes that were both privileged anyway, it might make sense to > re-enable it. But has this feature of the scheduler been maintained wel= l > enough for this to be a good idea? If not, would it worth looking into > updating it so that FreeBSD runs well on the Atom? It's as good as it can be on recent ULE2 scheduler. ULE2 has support for HTT but there's not much that can be done at the scheduler level as the Atom is single-socket, single-core CPU. Atom's HTT is actually pretty good - I saw up to 25% more performance simply by using multithreading in 7zip's compression benchmark (on WinXP, though). Of course, OTOH it uses about that much more transistors on the CPU die so it's not exactly free performance. --------------enig8F241890DBD490D25AC8994B Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (MingW32) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iEYEARECAAYFAklOxAwACgkQldnAQVacBcg+2ACfcdQR4tUuh4pjToLJAOq7Z8tA JTkAn0HBhmeKnjn8E5i2av7dTDJzEtSX =h2O/ -----END PGP SIGNATURE----- --------------enig8F241890DBD490D25AC8994B--
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