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([2001:b07:6468:f312:bc4e:7fe8:2916:6a59]) by smtp.gmail.com with ESMTPSA id m7sm4047716wma.39.2020.01.09.12.51.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 09 Jan 2020 12:51:53 -0800 (PST) Subject: Re: [PATCH v3 00/21] KVM: Dirty ring interface To: "Michael S. Tsirkin" , Peter Xu Cc: Alex Williamson , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Christophe de Dinechin , Sean Christopherson , Yan Zhao , Jason Wang , Kevin Kevin , Vitaly Kuznetsov , "Dr . David Alan Gilbert" , Kirti Wankhede References: <20200109145729.32898-1-peterx@redhat.com> <20200109094711.00eb96b1@w520.home> <20200109175808.GC36997@xz-x1> <20200109140948-mutt-send-email-mst@kernel.org> From: Paolo Bonzini Message-ID: Date: Thu, 9 Jan 2020 21:51:50 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <20200109140948-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/01/20 20:13, Michael S. Tsirkin wrote: > That's one of the reasons I called for using something > resembling vring_packed_desc. In principle it could make sense to use the ring-wrap detection mechanism from vring_packed_desc instead of the producer/consumer indices. However, the element address/length indirection is unnecessary. Also, unlike virtio, KVM needs to know if there are N free entries (N is ~512) before running a guest. I'm not sure if that is possible with ring-wrap counters, while it's trivial with producer/consumer indices. Paolo