From mboxrd@z Thu Jan 1 00:00:00 1970 From: Loic Prylli Subject: Re: howto use ioremap_wc? Date: Mon, 02 Jun 2008 14:18:04 -0400 Message-ID: <4844395C.2010900@myri.com> References: <4841143E.5080003@myri.com> <20080531185424.1cd18220@infradead.org> <48441F73.5040005@myri.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Arjan van de Ven , LKML , netdev@vger.kernel.org, "venkatesh.pallipadi@intel.com" To: Brice Goglin Return-path: Received: from mailbox2.myri.com ([64.172.73.26]:2004 "EHLO myri.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751602AbYFBSqb (ORCPT ); Mon, 2 Jun 2008 14:46:31 -0400 In-Reply-To: <48441F73.5040005@myri.com> Sender: netdev-owner@vger.kernel.org List-ID: On 06/02/2008 12:27 PM, Brice Goglin wrote: > Arjan van de Ven wrote: > >> Ok this leads to a question: since write combining is effectively an >> extension (eg relaxation) to uncached, how much do you care if you >> actually get uncached? Eg can you just use the "WC" function even for >> the case where you get an uncached mapping ? >> >> > > WC is strictly required for our "wcfifo" path, To be more accurate about the above statement, that codepath will still work correctly even if the mapping ends-up being uncached, but that could lead to a 16X slowdown on some machines, since that path was really designed for the WC case. Anyway that codepath does not really matter as Brice mentioned afterwards :-) > but this path is actually > not so important nowadays. It is disabled by default and might even be > removed in the future. So, no, myri10ge itself does not really need to > know whether the mapping is actually WC. > Loic