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Mon, 18 May 2020 04:51:10 -0700 (PDT) Received: from [192.168.178.58] ([151.30.90.67]) by smtp.gmail.com with ESMTPSA id m65sm16590858wmm.17.2020.05.18.04.51.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 18 May 2020 04:51:09 -0700 (PDT) Subject: Re: [PATCH 0/2] Expose KVM API to Linux Kernel To: Maxim Levitsky , Anastassios Nanos , Marc Zyngier References: <760e0927-d3a7-a8c6-b769-55f43a65e095@redhat.com> <680e86ca19dd9270b95917da1d65e4b4d2bb18a9.camel@redhat.com> From: Paolo Bonzini Message-ID: Date: Mon, 18 May 2020 13:51:07 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <680e86ca19dd9270b95917da1d65e4b4d2bb18a9.camel@redhat.com> Content-Language: en-US X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Cc: Thomas Gleixner , Wanpeng Li , kvm@vger.kernel.org, Catalin Marinas , Joerg Roedel , x86@kernel.org, linux-kernel@vger.kernel.org, Sean Christopherson , Ingo Molnar , "H. Peter Anvin" , Borislav Petkov , Vitaly Kuznetsov , Will Deacon , kvmarm@lists.cs.columbia.edu, Jim Mattson X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On 18/05/20 13:34, Maxim Levitsky wrote: >> In high-performance configurations, most of the time virtio devices are >> processed in another thread that polls on the virtio rings. In this >> setup, the rings are configured to not cause a vmexit at all; this has >> much smaller latency than even a lightweight (kernel-only) vmexit, >> basically corresponding to writing an L1 cache line back to L2. > > This can be used to run kernel drivers inside a very thin VM IMHO to break up the stigma, > that kernel driver is always a bad thing to and should be by all means replaced by a userspace driver, > something I see a lot lately, and what was the ground for rejection of my nvme-mdev proposal. It's a tought design decision between speeding up a kernel driver with something like eBPF or wanting to move everything to userspace. Networking has moved more towards the first because there are many more opportunities for NIC-based acceleration, while storage has moved towards the latter with things such as io_uring. That said, I don't see why in-kernel NVMeoF drivers would be acceptable for anything but Fibre Channel (and that's only because FC HBAs try hard to hide most of the SAN layers). Paolo _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm