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Peter Anvin" 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-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 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