From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH net-next-2.6] pcnet32: Remove pointless memory barriers Date: Tue, 28 Apr 2009 22:16:05 -0700 (PDT) Message-ID: <20090428.221605.71993506.davem@davemloft.net> References: <1240945659.8819.9.camel@Maple> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, pcnet32@verizon.net To: john.dykstra1@gmail.com Return-path: Received: from 74-93-104-97-Washington.hfc.comcastbusiness.net ([74.93.104.97]:57609 "EHLO sunset.davemloft.net" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1751472AbZD2FQM (ORCPT ); Wed, 29 Apr 2009 01:16:12 -0400 In-Reply-To: <1240945659.8819.9.camel@Maple> Sender: netdev-owner@vger.kernel.org List-ID: From: John Dykstra Date: Tue, 28 Apr 2009 19:07:39 +0000 > These two memory barriers in performance-critical paths are not needed > on x86. Even if some other architecture does buffer PCI I/O space > writes, the existing memory-mapped I/O barriers are unlikely to be what > is needed. > > Signed-off-by: John Dykstra Any driver where these things are present usually has them there for a reason. Usually it's because the SGI guys really did run into real problems without them on their huge machines which can reorder PCI MMIO wrt. real memory operations. I don't feel good applying this at all, given that I see no evidence that there has been any investigation into how these barriers got there in the first place.