Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751971AbaAOVb4 (ORCPT ); Wed, 15 Jan 2014 16:31:56 -0500 Received: from mail-vc0-f176.google.com ([209.85.220.176]:59357 "EHLO mail-vc0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751202AbaAOVbx (ORCPT ); Wed, 15 Jan 2014 16:31:53 -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 13:31:52 -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 1:20 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. -- Dan -- 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/