From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8AD95C07E96 for ; Thu, 8 Jul 2021 09:29:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 63D9D619C5 for ; Thu, 8 Jul 2021 09:29:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231460AbhGHJcD (ORCPT ); Thu, 8 Jul 2021 05:32:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38298 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231272AbhGHJcD (ORCPT ); Thu, 8 Jul 2021 05:32:03 -0400 Received: from theia.8bytes.org (8bytes.org [IPv6:2a01:238:4383:600:38bc:a715:4b6d:a889]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8853CC061574 for ; Thu, 8 Jul 2021 02:29:21 -0700 (PDT) Received: by theia.8bytes.org (Postfix, from userid 1000) id 3AF02312; Thu, 8 Jul 2021 11:29:20 +0200 (CEST) Date: Thu, 8 Jul 2021 11:29:18 +0200 From: Joerg Roedel To: David Stevens , Robin Murphy Cc: Will Deacon , Christoph Hellwig , Sergey Senozhatsky , iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, David Stevens Subject: Re: [PATCH 0/4] Add dynamic iommu backed bounce buffers Message-ID: References: <20210707075505.2896824-1-stevensd@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210707075505.2896824-1-stevensd@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Adding Robin too. On Wed, Jul 07, 2021 at 04:55:01PM +0900, David Stevens wrote: > Add support for per-domain dynamic pools of iommu bounce buffers to the > dma-iommu API. This allows iommu mappings to be reused while still > maintaining strict iommu protection. Allocating buffers dynamically > instead of using swiotlb carveouts makes per-domain pools more amenable > on systems with large numbers of devices or where devices are unknown. > > When enabled, all non-direct streaming mappings below a configurable > size will go through bounce buffers. Note that this means drivers which > don't properly use the DMA API (e.g. i915) cannot use an iommu when this > feature is enabled. However, all drivers which work with swiotlb=force > should work. > > Bounce buffers serve as an optimization in situations where interactions > with the iommu are very costly. For example, virtio-iommu operations in > a guest on a linux host require a vmexit, involvement the VMM, and a > VFIO syscall. For relatively small DMA operations, memcpy can be > significantly faster. > > As a performance comparison, on a device with an i5-10210U, I ran fio > with a VFIO passthrough NVMe drive with '--direct=1 --rw=read > --ioengine=libaio --iodepth=64' and block sizes 4k, 16k, 64k, and > 128k. Test throughput increased by 2.8x, 4.7x, 3.6x, and 3.6x. Time > spent in iommu_dma_unmap_(page|sg) per GB processed decreased by 97%, > 94%, 90%, and 87%. Time spent in iommu_dma_map_(page|sg) decreased > by >99%, as bounce buffers don't require syncing here in the read case. > Running with multiple jobs doesn't serve as a useful performance > comparison because virtio-iommu and vfio_iommu_type1 both have big > locks that significantly limit mulithreaded DMA performance. > > This patch set is based on v5.13-rc7 plus the patches at [1]. > > David Stevens (4): > dma-iommu: add kalloc gfp flag to alloc helper > dma-iommu: replace device arguments > dma-iommu: expose a few helper functions to module > dma-iommu: Add iommu bounce buffers to dma-iommu api > > drivers/iommu/Kconfig | 10 + > drivers/iommu/Makefile | 1 + > drivers/iommu/dma-iommu.c | 119 ++++-- > drivers/iommu/io-buffer-pool.c | 656 +++++++++++++++++++++++++++++++++ > drivers/iommu/io-buffer-pool.h | 91 +++++ > include/linux/dma-iommu.h | 12 + > 6 files changed, 861 insertions(+), 28 deletions(-) > create mode 100644 drivers/iommu/io-buffer-pool.c > create mode 100644 drivers/iommu/io-buffer-pool.h > > -- > 2.32.0.93.g670b81a890-goog