Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751514AbWCHXlH (ORCPT ); Wed, 8 Mar 2006 18:41:07 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751524AbWCHXlH (ORCPT ); Wed, 8 Mar 2006 18:41:07 -0500 Received: from gate.crashing.org ([63.228.1.57]:7563 "EHLO gate.crashing.org") by vger.kernel.org with ESMTP id S1751514AbWCHXlF (ORCPT ); Wed, 8 Mar 2006 18:41:05 -0500 Subject: Re: [PATCH] Define flush_wc, a way to flush write combining store buffers From: Benjamin Herrenschmidt To: "Bryan O'Sullivan" Cc: akpm@osdl.org, ak@suse.de, paulus@samba.org, bcrl@kvack.org, linux-kernel@vger.kernel.org In-Reply-To: <1141854208.27555.1.camel@localhost.localdomain> References: <1141853919.11221.183.camel@localhost.localdomain> <1141854208.27555.1.camel@localhost.localdomain> Content-Type: text/plain Date: Thu, 09 Mar 2006 10:40:29 +1100 Message-Id: <1141861230.11221.189.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.5.92 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1658 Lines: 38 On Wed, 2006-03-08 at 13:43 -0800, Bryan O'Sullivan wrote: > On Thu, 2006-03-09 at 08:38 +1100, Benjamin Herrenschmidt wrote: > > > I think people already don't undersatnd the existing gazillion of > > barriers we have with quite unclear semantics in some cases, it's not > > time to add a new one ... > > What do you suggest I do, then? This makes a substantial difference to > performance for us. Should I confine this somehow to the ipath driver > directory and have a nest of ifdefs in an include file there? What bothers me is that because of that exact same argument "it makes substantial difference for us", we end up with basically barriers tailored for architectures... that is as many kind of barriers as we have architectuers... like mmiowb :) Currently, PowerPC is losing significant performances for example to try to "fit" in the linux barriers for things like IOs which would leak out of spinlocks if we didn't have a strong barrier in pretty much every writeX() or things like that. We could use the same argument you are making to come up with yet another set of barriers that are more friendly to ppc ... At the end of the day, however, the problem is that pretty much no driver write understand anything about any of the barriers and get them all wrong... Which makes me thing we are trying to use the wrong tool or providing the wrong level of abstraction or something there... Ben. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/