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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3BAC0C52D6D for ; Wed, 31 Jul 2024 11:19:33 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1sZ7Lz-0006R4-OT; Wed, 31 Jul 2024 07:18:47 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sZ7Lx-0006Ma-2C for qemu-devel@nongnu.org; Wed, 31 Jul 2024 07:18:46 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sZ7Lv-0006nZ-Dy for qemu-devel@nongnu.org; Wed, 31 Jul 2024 07:18:44 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1722424720; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=2ZAdrir/XPqbfvH9QDX+kfny3g50pUo5BZS7PsDKhr8=; b=GVq3OWlAsZMhcx7Q81bYJj53etPH5W20yEnL1YPUR6K5FuwJIfb2q4PSBQo0dzu6575WMd zzUHonuJ7BV7M0tP0nplDoNWWjUfVRZqjzPeHzT1e64LHpXVw7uqP6IiTEC0NI8SnmDnYp gQIFW4qPRSFB21EbVqonn1Bn9OTMlj0= Received: from mail-ej1-f69.google.com (mail-ej1-f69.google.com [209.85.218.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-73-N5vA2C3VPi-KNeDl6O-BSQ-1; Wed, 31 Jul 2024 07:18:39 -0400 X-MC-Unique: N5vA2C3VPi-KNeDl6O-BSQ-1 Received: by mail-ej1-f69.google.com with SMTP id a640c23a62f3a-a7aaef3fdafso119655866b.1 for ; Wed, 31 Jul 2024 04:18:38 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1722424718; x=1723029518; h=content-transfer-encoding:in-reply-to:organization:autocrypt :content-language:from:references:cc:to:subject:user-agent :mime-version:date:message-id:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to; bh=2ZAdrir/XPqbfvH9QDX+kfny3g50pUo5BZS7PsDKhr8=; b=pl0tJrtoWBKpDxTMWYQulw27H7Q2Vz0hGGe8uYflcVDQfRItaXNc8/xNs3YqmD6wN2 dQ+vuXpOho/dUBUN65fnIHph4wwnJmt8e6DhLEd1ClqAFenZVrNdNewyxGsZ7OBxBdSP sbuNBGBzloousrx2afjMBjawIQ9UIpULLlY6CPozK/QTbaQDmlHK8qMm9hLBzjyWbanZ aFZqotrFEekjU+v7r5/Ncv6CzMp2QmMlT/x86R1D1oLi+hMLFECXZN1xBONW9ACxmL4z P3XBm34q9neGSZZr2IRq9CkbbKXmBz6PmJkMoYNAkN/1ziKe6efC3+v4vOeytwVCd2+v WMbw== X-Gm-Message-State: AOJu0YwsUnOeFbULT3pA1s+6gkX+mBWygZpyTid+LavGbArrf3P+A95E ERt0FueB8eFvQNUe7VsLcs98DO+tzDm1yK9IVEmFVjTqL1jbpOY8gs9rZCsB2fd+sZxCPd5RK31 B73TdpTkv87y8Nb6n42Edhs8HEifBHihOeitdai5cZB4nUaczP6wo X-Received: by 2002:a17:907:7f13:b0:a6f:6337:1ad5 with SMTP id a640c23a62f3a-a7d85a4c772mr473551466b.27.1722424717761; Wed, 31 Jul 2024 04:18:37 -0700 (PDT) X-Google-Smtp-Source: AGHT+IEtsbeRG2h5iQvMOcjjOiuOUIYF6sGKYeFbxW+JKxy4hY5/XZrj6Jyn1Ccfy7kOvO+24uK95A== X-Received: by 2002:a17:907:7f13:b0:a6f:6337:1ad5 with SMTP id a640c23a62f3a-a7d85a4c772mr473547766b.27.1722424717174; Wed, 31 Jul 2024 04:18:37 -0700 (PDT) Received: from ?IPV6:2003:cb:c70b:5f00:9b61:28a2:eea1:fa49? (p200300cbc70b5f009b6128a2eea1fa49.dip0.t-ipconnect.de. [2003:cb:c70b:5f00:9b61:28a2:eea1:fa49]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a7acad41484sm756980766b.124.2024.07.31.04.18.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 31 Jul 2024 04:18:36 -0700 (PDT) Message-ID: Date: Wed, 31 Jul 2024 13:18:35 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 0/6] Enable shared device assignment To: Chenyi Qiang , Paolo Bonzini , Peter Xu , =?UTF-8?Q?Philippe_Mathieu-Daud=C3=A9?= , Michael Roth Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org, Williams Dan J , Edgecombe Rick P , Wang Wei W , Peng Chao P , Gao Chao , Wu Hao , Xu Yilun References: <20240725072118.358923-1-chenyi.qiang@intel.com> <69091ee4-f1c9-43ce-8a2a-9bb370e8115f@intel.com> <0fdd0340-8daa-45b8-9e1c-bafe6f4e6a60@intel.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <0fdd0340-8daa-45b8-9e1c-bafe6f4e6a60@intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.126, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sorry for the late reply! >> Current users must skip it, yes. How private memory would have to be >> handled, and who would handle it, is rather unclear. >> >> Again, maybe we'd want separate RamDiscardManager for private and shared >> memory (after all, these are two separate memory backends). > > We also considered distinguishing the populate and discard operation for > private and shared memory separately. As in method 2 above, we mentioned > to add a new argument to indicate the memory attribute to operate on. > They seem to have a similar idea. Yes. Likely it's just some implementation detail. I think the following states would be possible: * Discarded in shared + discarded in private (not populated) * Discarded in shared + populated in private (private populated) * Populated in shared + discarded in private (shared populated) One could map these to states discarded/private/shared indeed. [...] >> I've had this talk with Intel, because the 4K granularity is a pain. I >> was told that ship has sailed ... and we have to cope with random 4K >> conversions :( >> >> The many mappings will likely add both memory and runtime overheads in >> the kernel. But we only know once we measure. > > In the normal case, the main runtime overhead comes from > private<->shared flip in SWIOTLB, which defaults to 6% of memory with a > maximum of 1Gbyte. I think this overhead is acceptable. In non-default > case, e.g. dynamic allocated DMA buffer, the runtime overhead will > increase. As for the memory overheads, It is indeed unavoidable. > > Will these performance issues be a deal breaker for enabling shared > device assignment in this way? I see the most problematic part being the dma_entry_limit and all of these individual MAP/UNMAP calls on 4KiB granularity. dma_entry_limit is "unsigned int", and defaults to U16_MAX. So the possible maximum should be 4294967296, and the default is 65535. So we should be able to have a maximum of 16 TiB shared memory all in 4KiB chunks. sizeof(struct vfio_dma) is probably something like <= 96 bytes, implying a per-page overhead of ~2.4%, excluding the actual rbtree. Tree lookup/modifications with that many nodes might also get a bit slower, but likely still tolerable as you note. Deal breaker? Not sure. Rather "suboptimal" :) ... but maybe unavoidable for your use case? -- Cheers, David / dhildenb