From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935140AbdDZV7u (ORCPT ); Wed, 26 Apr 2017 17:59:50 -0400 Received: from mx2.suse.de ([195.135.220.15]:55888 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751344AbdDZV7k (ORCPT ); Wed, 26 Apr 2017 17:59:40 -0400 Date: Wed, 26 Apr 2017 23:59:36 +0200 From: Joerg Roedel To: Shaohua Li Cc: linux-kernel@vger.kernel.org, gang.wei@intel.com, hpa@linux.intel.com, mingo@kernel.org, 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: <20170426215936.GT5077@suse.de> References: <1c2cadcf5cd7d19cea93c56435610e61b551bd1e.1493223474.git.shli@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1c2cadcf5cd7d19cea93c56435610e61b551bd1e.1493223474.git.shli@fb.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.