From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by vger.rutgers.edu via listexpand id ; Tue, 25 Jan 2000 10:38:26 -0500 Received: by vger.rutgers.edu id ; Tue, 25 Jan 2000 10:34:24 -0500 Received: from smtp6.mindspring.com ([207.69.200.110]:2534 "EHLO smtp6.mindspring.com") by vger.rutgers.edu with ESMTP id ; Tue, 25 Jan 2000 10:33:36 -0500 Message-ID: <388DFBD8.5A89B100@10xinc.com> Date: Tue, 25 Jan 2000 11:39:04 -0800 From: Iain McClatchie Organization: 10x X-Mailer: Mozilla 4.6 [en] (X11; I; Linux 2.2.12 i686) X-Accept-Language: en MIME-Version: 1.0 To: Larry McVoy Cc: linux-kernel@vger.rutgers.edu Subject: Re: SMP Theory (was: Re: Interesting analysis of linux kernel threading by IBM) Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-linux-kernel@vger.rutgers.edu One of the problems with this forum is that you can't hear the murmur of assent ripple through the hardware design crowd when Larry rants about this stuff. Larry has had his head out of the box for a long time. Look at the ASCI project. The intention was for SGI to build an Origin with around 1000 CPUs. That Origin had extra cache coherence directory RAM and special encodings in that RAM so that the hardware could actually keep the memory across all 1000 CPUs coherent. We added extra physical address bits to the R10K to make this machine possible. Last I heard, the machine is mostly programmed with message passing. I remember having a talk with an O/S guy who was implementing some sort of message delivery utility inside the O/S. This was when Cellular IRIX was in development, and they were investigating having the various O/S images talk to each other with messages across the shared memory. Then someone found out the O/S images could signal each other FASTER through the HIPPI connections than they could through shared memory. That is, this machine had a HIPPI port local to each O/S image, and all those HIPPI ports were connected together via a HIPPI switch. Those HIPPI connections were build with the _same_physical_link_ as the shared memory - an 800 MB/s source-synchronous channel. But if you're sending a message, it's better to have the I/O system just send the bits one way than have the shared memory system do two round trips, one to invalidate the mailbox buffer for writing and another to process the remote cache miss to receive the message. -Iain McClatchie www.10xinc.com iain@10xinc.com 650-364-0520 voice 650-364-0530 FAX - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.rutgers.edu Please read the FAQ at http://www.tux.org/lkml/