From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752591AbYLROeo (ORCPT ); Thu, 18 Dec 2008 09:34:44 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751790AbYLROeb (ORCPT ); Thu, 18 Dec 2008 09:34:31 -0500 Received: from mga09.intel.com ([134.134.136.24]:56101 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751660AbYLROea convert rfc822-to-8bit (ORCPT ); Thu, 18 Dec 2008 09:34:30 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.36,243,1228118400"; d="scan'208";a="475079768" From: "Sosnowski, Maciej" To: "Williams, Dan J" CC: "linux-kernel@vger.kernel.org" , "netdev@vger.kernel.org" , "hskinnemoen@atmel.com" , "g.liakhovetski@gmx.de" , "nicolas.ferre@atmel.com" Date: Thu, 18 Dec 2008 14:34:18 +0000 Subject: RE: [PATCH 11/13] dmaengine: kill struct dma_client and supporting infrastructure Thread-Topic: [PATCH 11/13] dmaengine: kill struct dma_client and supporting infrastructure Thread-Index: AclfEpW2QtLwhWoSTIOuSph3uJB/LACBprJQ Message-ID: <129600E5E5FB004392DDC3FB599660D70C984F6E@irsmsx504.ger.corp.intel.com> References: <20081114213300.32354.1154.stgit@dwillia2-linux.ch.intel.com> <20081114213513.32354.58256.stgit@dwillia2-linux.ch.intel.com> <129600E5E5FB004392DDC3FB599660D70C8F3407@irsmsx504.ger.corp.intel.com> In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: en-US Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Dan Williams wrote: > On Fri, Dec 12, 2008 at 7:29 AM, Sosnowski, Maciej > wrote: >> Williams, Dan J wrote: >>> All users have been converted to either the general-purpose >>> allocator, dma_find_channel, or dma_request_channel. >>> >>> Signed-off-by: Dan Williams >>> --- >> (...) >>> /** >>> - * dma_chans_notify_available - broadcast available channels to >>> the clients >>> - */ >>> -static void dma_clients_notify_available(void) >>> -{ >>> - struct dma_client *client; >>> - >>> - mutex_lock(&dma_list_mutex); >>> - >>> - list_for_each_entry(client, &dma_client_list, global_node) >>> - dma_client_chan_alloc(client); >>> - >>> - mutex_unlock(&dma_list_mutex); >>> -} >> >> I agree with Guennadi's concern about removing clients' notification >> of new devices available in the system. >> I understand that this design is based on polling instead, >> however polling is always less efficient approach. >> Do you think that restoring notifications in this redesigned >> dmaengine would be more painful than limiting clients to polling >> solution? >> > > You are missing that net_dma has always "polled". Consider the case > of how net_dma currently operates prior to ioatdma.ko being loaded. > It periodically calls get_softnet_dma() to see if a channel is > available, if it does not find one it falls back to a cpu copy. All > that has changed is replacing this custom channel allocation routine > with the unified dma_find_channel() interface. Channel notifications > are not required. Either everything is built-in to guarantee that an > engine is available upon request[1], or the client is smart enough to > run without a channel for while like net_dma and raid offload. My comment here was rather more general than ioatdma/net_dma specific. You are of course right that net_dma has been always based on polling. I am rather worrying a bit that this change limits all current and future clients to polling approach only, not letting them base on notifications anymore. > > Regards, > Dan > > [1] http://marc.info/?l=linux-kernel&m=122835195303213&w=2 Regards, Maciej