From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Mosberger Date: Wed, 12 Jan 2005 21:54:51 +0000 Subject: RE: pgprot_writecombine & shub 1.x Message-Id: <16869.40107.667336.912445@napali.hpl.hp.com> List-Id: References: <200501111200.02504.jbarnes@sgi.com> In-Reply-To: <200501111200.02504.jbarnes@sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org >>>>> On Wed, 12 Jan 2005 20:31:30 +0100 (CET), Hugo Kohmann said: Hugo> Is there any new plans to implement support for writecombine Hugo> in kernel space ? I don't know of anybody who's working on it at the moment. Hugo> We have implemented a new socket transport family, AF_SCI, Hugo> that provides UDP/TCP compliant transport over SCI that needs Hugo> writecombine to archieve max througpht and low latency for Hugo> small messages. Large messages can be send using DMA, but Hugo> small messages highly benefit from memory mapped Hugo> transmission.... I think there are two somewhat separate issues here: (1) WC mapping of uncachable address-ranges. (2) WC mapping of memory. (1) isn't much of an issue (at least for today's chips; I think we may still be violating the architecture if we end up mapping the same address-range both UC and WC, but current chips don't care, AFAIK). (2) is where things get trickier. You'd have to make sure that any memory that's mapped WC is allocated in granule-sized chunks. There is no support for this at the moment. I do think it might be worthwhile to support this, but don't know of anybody working on it. --david