Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752090AbaAOVd4 (ORCPT ); Wed, 15 Jan 2014 16:33:56 -0500 Received: from mail-ve0-f180.google.com ([209.85.128.180]:61412 "EHLO mail-ve0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750937AbaAOVdx (ORCPT ); Wed, 15 Jan 2014 16:33:53 -0500 MIME-Version: 1.0 In-Reply-To: References: <20140114004509.27138.50345.stgit@viggo.jf.intel.com> <20140114004622.27138.54103.stgit@viggo.jf.intel.com> Date: Wed, 15 Jan 2014 13:33:52 -0800 Message-ID: Subject: Re: [PATCH v3 1/4] net_dma: simple removal From: Dan Williams To: saeed bishara Cc: "dmaengine@vger.kernel.org" , Alexander Duyck , Dave Jiang , Vinod Koul , "netdev@vger.kernel.org" , David Whipple , lkml , "David S. Miller" Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 15, 2014 at 1:31 PM, Dan Williams wrote: > On Wed, Jan 15, 2014 at 1:20 PM, saeed bishara wrote: >> Hi Dan, >> >> I'm using net_dma on my system and I achieve meaningful performance >> boost when running Iperf receive. >> >> As far as I know the net_dma is used by many embedded systems out >> there and might effect their performance. >> Can you please elaborate on the exact scenario that cause the memory corruption? >> >> Is the scenario mentioned here caused by "real life" application or >> this is more of theoretical issue found through manual testing, I was >> trying to find the thread describing the failing scenario and couldn't >> find it, any pointer will be appreciated. > > Did you see the referenced commit? > > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=77873803363c > > This is a real issue in that any app that forks() while receiving data > can cause the dma data to be lost. The problem is that the copy > operation falls back to cpu at many locations. Any one of those > instance could touch a mapped page and trigger a copy-on-write event. > The dma completes to the wrong location. > Btw, do you have benchmark data showing that NET_DMA is beneficial on these platforms? I would have expected worse performance on platforms without i/o coherent caches. -- 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/