Received: with ECARTIS (v1.0.0; list netdev); Thu, 07 Jul 2005 20:02:24 -0700 (PDT) Received: from sunset.davemloft.net (dsl027-180-168.sfo1.dsl.speakeasy.net [216.27.180.168]) by oss.sgi.com (8.12.10/8.12.10/SuSE Linux 0.7) with ESMTP id j6832KH9015383 for ; Thu, 7 Jul 2005 20:02:21 -0700 Received: from localhost ([127.0.0.1] ident=davem) by sunset.davemloft.net with esmtp (Exim 4.50) id 1Dqj6Q-0002d2-Fm; Thu, 07 Jul 2005 20:00:34 -0700 Date: Thu, 07 Jul 2005 20:00:34 -0700 (PDT) Message-Id: <20050707.200034.74747399.davem@davemloft.net> To: raghavendra.koushik@neterion.com Cc: akepner@sgi.com, jgarzik@pobox.com, netdev@oss.sgi.com, netdev@vger.kernel.org, ravinandan.arakali@neterion.com, leonid.grossman@neterion.com, rapuru.sriram@neterion.com Subject: Re: [PATCH 2.6.12.1 5/12] S2io: Performance improvements From: "David S. Miller" In-Reply-To: <200507080106.j6816NKP022996@guinness.s2io.com> References: <200507080106.j6816NKP022996@guinness.s2io.com> X-Mailer: Mew version 4.2 on Emacs 21.4 / Mule 5.0 (SAKAKI) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-archive-position: 2695 X-ecartis-version: Ecartis v1.0.0 Sender: netdev-bounce@oss.sgi.com Errors-to: netdev-bounce@oss.sgi.com X-original-sender: davem@davemloft.net Precedence: bulk X-list: netdev Content-Length: 526 Lines: 14 From: "Raghavendra Koushik" Date: Thu, 7 Jul 2005 18:06:19 -0700 > wmb() is to ensure ordered PIO writes. wmb() does no such thing. It only has influence on load and store instructions done by the local processor, it has no effect on what the PCI bus may do with PIO writes (ie. post them). If you need a PIO to complete in a specific order, you have to read it back. If you need PIO operations to occur in a specific order wrt. cpu memory operations, mmiowb() is what you need to use.