From owner-freebsd-smp Sun Feb 2 12:52:11 1997 Return-Path: Received: (from root@localhost) by freefall.freebsd.org (8.8.5/8.8.5) id MAA12591 for smp-outgoing; Sun, 2 Feb 1997 12:52:11 -0800 (PST) Received: from caipfs.rutgers.edu (root@caipfs.rutgers.edu [128.6.155.100]) by freefall.freebsd.org (8.8.5/8.8.5) with ESMTP id MAA12530 for ; Sun, 2 Feb 1997 12:52:02 -0800 (PST) Received: from jenolan.caipgeneral (jenolan.rutgers.edu [128.6.111.5]) by caipfs.rutgers.edu (8.7.6/8.7.3) with SMTP id PAA08996; Sun, 2 Feb 1997 15:51:02 -0500 (EST) Received: by jenolan.caipgeneral (SMI-8.6/SMI-SVR4) id PAA19542; Sun, 2 Feb 1997 15:50:45 -0500 Date: Sun, 2 Feb 1997 15:50:45 -0500 Message-Id: <199702022050.PAA19542@jenolan.caipgeneral> From: "David S. Miller" To: terry@lambert.org CC: terry@lambert.org, michaelh@cet.co.jp, netdev@roxanne.nuclecu.unam.mx, roque@di.fc.ul.pt, freebsd-smp@freebsd.org, smpdev@roxanne.nuclecu.unam.mx In-reply-to: <199702022042.NAA08516@phaeton.artisoft.com> (message from Terry Lambert on Sun, 2 Feb 1997 13:42:32 -0700 (MST)) Subject: Re: SMP Sender: owner-smp@freebsd.org X-Loop: FreeBSD.org Precedence: bulk From: Terry Lambert Date: Sun, 2 Feb 1997 13:42:32 -0700 (MST) Are you claiming that CPU2 would see the write of CPU1's cache line in all cases, and invalidate it's own cache line? Isn't there a potential race? I know it's unlikely, but it exists, right? This is the classic "Writeback Cancellation Requirement", and all cache coherency hardware implementations do have to deal with it somehow. Check out section 7.10.3 of the UltraSparc Programmers Manual, in the "UltraSPARC-I External Interfaces" chapter to see how one implementation happens to deal the race very nicely. The P_Reply and S_Reply signal synchronization rules are extremely clever here. ---------------------------------------------//// Yow! 11.26 MB/s remote host TCP bandwidth & //// 199 usec remote TCP latency over 100Mb/s //// ethernet. Beat that! //// -----------------------------------------////__________ o David S. Miller, davem@caip.rutgers.edu /_____________/ / // /_/ ><