Date: Thu, 23 Jul 2009 22:22:40 +0200 From: Ivan Voras <ivoras@freebsd.org> To: freebsd-questions@freebsd.org Subject: Re: ULE and Prescott question Message-ID: <h4agqp$oli$1@ger.gmane.org> In-Reply-To: <20090723132200.4cf4002e@gumby.homeunix.com> References: <200907221157.n6MBvpKf028533@mp.cs.niu.edu> <h47t3h$a69$1@ger.gmane.org> <20090723132200.4cf4002e@gumby.homeunix.com>
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This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig4E7529443CA8D9956615188F Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable RW wrote: > On Wed, 22 Jul 2009 22:33:46 +0200 > Ivan Voras <ivoras@freebsd.org> wrote: >=20 >> Scott Bennett wrote: >>> This is a curiousity question. I'm running 7.2-STABLE at >>> present on an old Inspiron XPS, which has a 3.4 GHz P4 Prescott >>> CPU. I have hyperthreading enabled in the kernel. The question >>> is: is there any appreciable performance difference to be expected >>> with this hardware setup between the ULE scheduler and the 4BSD >>> scheduler? Or does the fact that there is only one core eliminate >>> any difference in performance characteristics? >> I'd guess the second thing. It's not like there's cache to be shared >> between cores, etc.=20 >=20 > But with hyperthreading enabled, don't you have virtual CPUs sharing > L1 cache=20 Yes, > rather that cores sharing L2 cache, making the case for ULE > even stronger? If you're thinking about ULEs "soft-pinning" of processes to CPUs then I don't think so for two reasons: it's not like 4BSD forces processes ping-ponging everywhere - for 2 logical CPUs it's not that there's much choice of where to schedule a process - and thread switches between HTT logical CPUs is supposed to be cheap - I think since the L1 is shared, HTT cores have access to cached data from "the other" core for no cost. --------------enig4E7529443CA8D9956615188F 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/ iEYEARECAAYFAkpoxpUACgkQldnAQVacBciYiACgpsIA46bDyU8zejev+6TCpRXv b5wAn3uoF5X8zYkQ2A0cGnCqxCRgUns8 =rMJL -----END PGP SIGNATURE----- --------------enig4E7529443CA8D9956615188F--
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