From mboxrd@z Thu Jan 1 00:00:00 1970 Received: by oss.sgi.com id ; Wed, 19 Jan 2000 09:10:28 -0800 Received: from pneumatic-tube.sgi.com ([204.94.214.22]:27460 "EHLO pneumatic-tube.sgi.com") by oss.sgi.com with ESMTP id ; Wed, 19 Jan 2000 09:10:13 -0800 Received: from cthulhu.engr.sgi.com (cthulhu.engr.sgi.com [192.26.80.2]) by pneumatic-tube.sgi.com (980327.SGI.8.8.8-aspam/980310.SGI-aspam) via ESMTP id JAA07535; Wed, 19 Jan 2000 09:14:32 -0800 (PST) mail_from (owner-linux@cthulhu.engr.sgi.com) Received: (from majordomo-owner@localhost) by cthulhu.engr.sgi.com (980427.SGI.8.8.8/970903.SGI.AUTOCF) id IAA13621 for linux-list; Wed, 19 Jan 2000 08:58:55 -0800 (PST) mail_from (owner-linux@relay.engr.sgi.com) Received: from sgi.com (sgi.engr.sgi.com [192.26.80.37]) by cthulhu.engr.sgi.com (980427.SGI.8.8.8/970903.SGI.AUTOCF) via ESMTP id IAA65552 for ; Wed, 19 Jan 2000 08:58:35 -0800 (PST) mail_from (jharrell@ti.com) Received: from tower.ti.com (tower.ti.com [192.94.94.5]) by sgi.com (980327.SGI.8.8.8-aspam/980304.SGI-aspam: SGI does not authorize the use of its proprietary systems or networks for unsolicited or bulk email from the Internet.) via ESMTP id IAA02043 for ; Wed, 19 Jan 2000 08:58:14 -0800 (PST) mail_from (jharrell@ti.com) Received: from dlep6.itg.ti.com ([157.170.188.9]) by tower.ti.com (8.9.3/8.9.3) with ESMTP id KAA16824; Wed, 19 Jan 2000 10:58:03 -0600 (CST) Received: from dlep6.itg.ti.com (localhost [127.0.0.1]) by dlep6.itg.ti.com (8.9.3/8.9.3) with ESMTP id KAA16500; Wed, 19 Jan 2000 10:57:58 -0600 (CST) Received: from dlep4.itg.ti.com (dlep4.itg.ti.com [157.170.188.63]) by dlep6.itg.ti.com (8.9.3/8.9.3) with ESMTP id KAA16488; Wed, 19 Jan 2000 10:57:57 -0600 (CST) Received: from ti.com (IDENT:jharrell@pcp97780pcs.sc.ti.com [158.218.100.100]) by dlep4.itg.ti.com (8.9.3/8.9.3) with ESMTP id KAA26345; Wed, 19 Jan 2000 10:58:01 -0600 (CST) Message-ID: <3885ED9B.C8969F26@ti.com> Date: Wed, 19 Jan 2000 10:00:11 -0700 From: Jeff Harrell X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.2.12-20 i686) X-Accept-Language: en MIME-Version: 1.0 To: sgi-mips CC: Ralf Baechle , bbrown , vwells , kmcdonald , mhassler Subject: Question concerning cache coherency Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-linuxmips@oss.sgi.com Precedence: bulk Return-Path: X-Orcpt: rfc822;linuxmips-outgoing I have an interesting issue that I would like to run past the MIPS/Linux newsgroup. I am currently porting the MIPS/Linux code to a development board that has a IDT64475 MIPS core (64-bit R4xxx core). I notice that this part does not have any method of maintaining cache coherency (i.e., no hardware support for cache coherency). It is highly likely that we will be plugging in a network card on a PCI bus that would be DMA'ing to a shared memory space in SDRAM. I assume that the problem of cache coherency is fixed by mapping the shared memory as uncached. I have not dug into the network drivers (or the kernel) enough to know whether this is how the problem is addressed on typical MIPS architectures. I guess I have two questions related to this issue; Do devices that DMA, typically access uncached memory and if so, is a second buffer required to copy from kernel to user space? The second question is concerning the performance hit in running out of uncached memory, Have people seen significant performance degradation when using uncached memory. Any insight that anybody can provide would be greatly appreciated. Thanks, Jeff -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Jeff Harrell Work: (801) 619-6104 Broadband Access group/TI jharrell@ti.com ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~