From mboxrd@z Thu Jan 1 00:00:00 1970 From: tlaronde@polynum.com Date: Fri, 17 Apr 2009 20:18:48 +0200 To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net> Message-ID: <20090417181848.GA3033@polynum.com> References: <21493d85b69b070fed0a4f864eb5325a@proxima.alt.za> <57928816a76e769327ca134d7e28bd06@bellsouth.net> <20090417171154.GA2029@polynum.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.3i Content-Transfer-Encoding: quoted-printable Subject: Re: [9fans] VMs, etc. (was: Re: security questions) Topicbox-Message-UUID: e278172e-ead4-11e9-9d60-3106f5b1d025 On Fri, Apr 17, 2009 at 01:29:09PM -0400, erik quanstrom wrote: > > In some sense, logically (but not efficiently: read the caveats in th= e > > Plan9 papers; a processor is nothing without tightly coupled memory, = so > > memory is not a remote pool sharable---Mach!),=20 >=20 > if you look closely enough, this kind of breaks down. numa > machines are pretty popular these days (opteron, intel qpi-based > processors). it's possible with a modest loss of performance to > share memory across processors and not worry about it. NUMA are, from my point of view, "tightly" connected. By loosely, I mean a memory accessed by non dedicated processor=20 hardware means (if this makes sense). Moving data from different memories via some IP based protocol or worse. But all in all, finally a copy is put in the tightly connected memory, whether huge caches, or dedicated main memory. The disaster of Mach (I don't know if my bad english is responsible for this, but in the Plan9 paper the "research" or "university" OS that is implicitely gibed at is Mach) is a kind of example. NUMA are sufficiently special beasts that the majority of huge computing facilities have been done by clusters (because it was easier for software only organizations). This definitively doesn't mean NUMA has no raison d'=EAtre. On the contrary, this is an argument supplementary to the distinction between the UI (terminals) and the CPU. --=20 Thierry Laronde (Alceste) http://www.kergis.com/ Key fingerprint =3D 0FF7 E906 FBAF FE95 FD89 250D 52B1 AE95 6006 F40C