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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 80DB3C61DA4 for ; Mon, 6 Feb 2023 11:21:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229632AbjBFLV3 (ORCPT ); Mon, 6 Feb 2023 06:21:29 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39250 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229875AbjBFLVX (ORCPT ); Mon, 6 Feb 2023 06:21:23 -0500 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 9ACA722DE7; Mon, 6 Feb 2023 03:21:02 -0800 (PST) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 828E5C14; Mon, 6 Feb 2023 03:21:32 -0800 (PST) Received: from [10.57.89.151] (unknown [10.57.89.151]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8AD653F8C6; Mon, 6 Feb 2023 03:20:48 -0800 (PST) Message-ID: <4d90da14-8c08-62e1-814f-ee14fab375f8@arm.com> Date: Mon, 6 Feb 2023 11:20:44 +0000 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:102.0) Gecko/20100101 Thunderbird/102.6.1 Subject: Re: [PATCH] iommu/vt-d: Avoid superfluous IOTLB tracking in lazy mode Content-Language: en-GB To: Baolu Lu , Jacob Pan , LKML , iommu@lists.linux.dev, Joerg Roedel Cc: David Woodhouse , Raj Ashok , "Tian, Kevin" , Yi Liu , stable@vger.kernel.org, Sanjay Kumar References: <20230203230417.1287325-1-jacob.jun.pan@linux.intel.com> From: Robin Murphy In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2023-02-04 06:32, Baolu Lu wrote: > On 2023/2/4 7:04, Jacob Pan wrote: >> Intel IOMMU driver implements IOTLB flush queue with domain selective >> or PASID selective invalidations. In this case there's no need to track >> IOVA page range and sync IOTLBs, which may cause significant performance >> hit. > > [Add cc Robin] > > If I understand this patch correctly, this might be caused by below > helper: > > /** >  * iommu_iotlb_gather_add_page - Gather for page-based TLB invalidation >  * @domain: IOMMU domain to be invalidated >  * @gather: TLB gather data >  * @iova: start of page to invalidate >  * @size: size of page to invalidate >  * >  * Helper for IOMMU drivers to build invalidation commands based on > individual >  * pages, or with page size/table level hints which cannot be gathered > if they >  * differ. >  */ > static inline void iommu_iotlb_gather_add_page(struct iommu_domain *domain, >                                                struct > iommu_iotlb_gather *gather, >                                                unsigned long iova, > size_t size) > { >         /* >          * If the new page is disjoint from the current range or is > mapped at >          * a different granularity, then sync the TLB so that the gather >          * structure can be rewritten. >          */ >         if ((gather->pgsize && gather->pgsize != size) || >             iommu_iotlb_gather_is_disjoint(gather, iova, size)) >                 iommu_iotlb_sync(domain, gather); > >         gather->pgsize = size; >         iommu_iotlb_gather_add_range(gather, iova, size); > } > > As the comments for iommu_iotlb_gather_is_disjoint() says, > > "...For many IOMMUs, flushing the IOMMU in this case is better >  than merging the two, which might lead to unnecessary invalidations. >  ..." > > So, perhaps the right fix for this performance issue is to add > >     if (!gather->queued) > > in iommu_iotlb_gather_add_page() or iommu_iotlb_gather_is_disjoint()? > It should benefit other arch's as well. The iotlb_gather helpers are really just that - little tools to help drivers with various common iotlb_gather accounting patterns. The decision whether to bother with that accounting at all should really come beforehand, and whether a driver supports flush queues is orthogonal to whether it uses any particular gather helper(s) or not, so I think the patch as-is is correct. >> This patch adds a check to avoid IOVA gather page and IOTLB sync for >> the lazy path. >> >> The performance difference on Sapphire Rapids 100Gb NIC is improved by >> the following (as measured by iperf send): > > Which test case have you done? Post the real data if you have any. > >> >> w/o this fix~48 Gbits/s. with this fix ~54 Gbits/s >> >> Cc: > > Again, add a Fixes tag so that people know how far this fix should be > back ported. Note that the overall issue probably dates back to the initial iommu-dma conversion, but if you think it's important enough to go back beyond 5.15 when gather->queued was introduced, that'll need a different fix. Cheers, Robin.