On Thu, Mar 21, 2019 at 07:07:38PM +0200, Maxim Levitsky wrote: > On Thu, 2019-03-21 at 16:13 +0000, Stefan Hajnoczi wrote: > > On Tue, Mar 19, 2019 at 04:41:07PM +0200, Maxim Levitsky wrote: > > > Date: Tue, 19 Mar 2019 14:45:45 +0200 > > > Subject: [PATCH 0/9] RFC: NVME VFIO mediated device > > > > > > Hi everyone! > > > > > > In this patch series, I would like to introduce my take on the problem of > > > doing > > > as fast as possible virtualization of storage with emphasis on low latency. > > > > > > In this patch series I implemented a kernel vfio based, mediated device > > > that > > > allows the user to pass through a partition and/or whole namespace to a > > > guest. > > > > > > The idea behind this driver is based on paper you can find at > > > https://www.usenix.org/conference/atc18/presentation/peng, > > > > > > Although note that I stared the development prior to reading this paper, > > > independently. > > > > > > In addition to that implementation is not based on code used in the paper > > > as > > > I wasn't being able at that time to make the source available to me. > > > > > > ***Key points about the implementation:*** > > > > > > * Polling kernel thread is used. The polling is stopped after a > > > predefined timeout (1/2 sec by default). > > > Support for all interrupt driven mode is planned, and it shows promising > > > results. > > > > > > * Guest sees a standard NVME device - this allows to run guest with > > > unmodified drivers, for example windows guests. > > > > > > * The NVMe device is shared between host and guest. > > > That means that even a single namespace can be split between host > > > and guest based on different partitions. > > > > > > * Simple configuration > > > > > > *** Performance *** > > > > > > Performance was tested on Intel DC P3700, With Xeon E5-2620 v2 > > > and both latency and throughput is very similar to SPDK. > > > > > > Soon I will test this on a better server and nvme device and provide > > > more formal performance numbers. > > > > > > Latency numbers: > > > ~80ms - spdk with fio plugin on the host. > > > ~84ms - nvme driver on the host > > > ~87ms - mdev-nvme + nvme driver in the guest > > > > You mentioned the spdk numbers are with vhost-user-nvme. Have you > > measured SPDK's vhost-user-blk? > > I had lot of measuments of vhost-user-blk vs vhost-user-nvme. > vhost-user-nvme was always a bit faster but only a bit. > Thus I don't think it makes sense to benchamrk against vhost-user-blk. It's interesting because mdev-nvme is closest to the hardware while vhost-user-blk is closest to software. Doing things at the NVMe level isn't buying much performance because it's still going through a software path comparable to vhost-user-blk. From what you say it sounds like there isn't much to optimize away :(. Stefan
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