From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752207AbbFHLpJ (ORCPT ); Mon, 8 Jun 2015 07:45:09 -0400 Received: from mga01.intel.com ([192.55.52.88]:18273 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751081AbbFHLpA (ORCPT ); Mon, 8 Jun 2015 07:45:00 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.13,573,1427785200"; d="scan'208";a="742935276" Message-ID: <5575802B.5070906@linux.intel.com> Date: Mon, 08 Jun 2015 19:44:43 +0800 From: Jiang Liu Organization: Intel User-Agent: Mozilla/5.0 (Windows NT 6.2; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: Vinod Koul CC: Dave Jiang , Dan Williams , Jarkko Nikula , "Rafael J. Wysocki" , David Woodhouse , Tony Luck , x86@kernel.org, linux-kernel@vger.kernel.org, dmaengine@vger.kernel.org Subject: Re: [RFC Patch V1] ioatdma: Ignore IOAT devices under hotplug-capable PCI host bridge References: <1433226969-8748-1-git-send-email-jiang.liu@linux.intel.com> <556D4F2B.5040107@linux.intel.com> <20150608104234.GF28601@localhost> In-Reply-To: <20150608104234.GF28601@localhost> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2015/6/8 18:42, Vinod Koul wrote: > On Tue, Jun 02, 2015 at 02:37:31PM +0800, Jiang Liu wrote: >> Ccing Rafael, it's ACPI hotplug related. >> >> On 2015/6/2 14:36, Jiang Liu wrote: >>> The dmaengine core assumes that async DMA devices will only be removed >>> when they not used anymore, or it assumes dma_async_device_unregister() >>> will only be called by dma driver exit routines. But this assumption is >>> not true for the IOAT driver, which calls dma_async_device_unregister() >>> from ioat_remove(). So current IOAT driver doesn't support device >>> hot-removal because it may cause system crash to hot-remove an inuse >>> IOAT device. >>> >>> To support CPU socket hot-removal, all PCI devices, including IOAT >>> devices embedded in the socket, will be hot-removed. The idea solution >>> is to enhance the dmaengine core and IOAT driver to support hot-removal, >>> but that's too hard. >>> >>> This patch implements a hack to disable IOAT devices under hotplug-capable >>> CPU socket so it won't break socket hot-removal. >>> > So below looks okay though I wonder how hard would it be to fix hot unplug ? Hi Vinod, Thanks for review. About three years ago I worked out a patch set to enhance the dmaengine core and ioat device driver to support hot-removal. But it has been rejected due to concerns about performance penalty caused by usage tracking. To support hot-removal, we need to track dma channel usage and a way to reclaim dma channels when hot-removing. This may cause sensible performance penalty. Recently I have tried again but still haven't find a way to support hot-removal. So eventually I suggest to disable IOAT device on hot-plug capable systems. Thanks! Gerry