Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1162391AbdD0GxM (ORCPT ); Thu, 27 Apr 2017 02:53:12 -0400 Received: from mail-wm0-f67.google.com ([74.125.82.67]:34545 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1162376AbdD0Gw5 (ORCPT ); Thu, 27 Apr 2017 02:52:57 -0400 Date: Thu, 27 Apr 2017 08:52:53 +0200 From: Ingo Molnar To: Joerg Roedel Cc: Shaohua Li , linux-kernel@vger.kernel.org, gang.wei@intel.com, hpa@linux.intel.com, kernel-team@fb.com, ning.sun@intel.com, srihan@fb.com, alex.eydelberg@intel.com Subject: Re: [PATCH V2] x86/tboot: add an option to disable iommu force on Message-ID: <20170427065253.zuq4a43girwcsotu@gmail.com> References: <1c2cadcf5cd7d19cea93c56435610e61b551bd1e.1493223474.git.shli@fb.com> <20170426215936.GT5077@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170426215936.GT5077@suse.de> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1289 Lines: 30 * Joerg Roedel wrote: > On Wed, Apr 26, 2017 at 09:18:35AM -0700, Shaohua Li wrote: > > IOMMU harms performance signficantly when we run very fast networking > > workloads. It's 40GB networking doing XDP test. Software overhead is > > almost unaware, but it's the IOTLB miss (based on our analysis) which > > kills the performance. We observed the same performance issue even with > > software passthrough (identity mapping), only the hardware passthrough > > survives. The pps with iommu (with software passthrough) is only about > > ~30% of that without it. This is a limitation in hardware based on our > > observation, so we'd like to disable the IOMMU force on, but we do want > > to use TBOOT and we can sacrifice the DMA security bought by IOMMU. I > > must admit I know nothing about TBOOT, but TBOOT guys (cc-ed) think not > > eabling IOMMU is totally ok. > > > > So introduce a new boot option to disable the force on. It's kind of > > silly we need to run into intel_iommu_init even without force on, but we > > need to disable TBOOT PMR registers. For system without the boot option, > > nothing is changed. > > > > Signed-off-by: Shaohua Li > > Applied, thanks. Please don't apply it yet, I posted a few review questions. Thanks, Ingo