We're hiring!
*

NVMe: Officially faster for emulated controllers!

Helen Koike avatar

Helen Koike
June 13, 2017

Share this post:

The Doorbell Buffer Config command

When I last wrote about NVMe, the feature to improve NVMe performance over emulated environments was just a living discussion and a work in progress patch. However, it has now been officially released in the NVMe Specification Revision 1.3 under the name "Doorbell Buffer Config command", along with an implementation that is already in the mainline Linux kernel! \o/

You can already feel the difference in performance if you compile Kernel 4.12-rc1 (or later) and run it over a virtual machine hosted on Google Compute Engine. Google actually updated their hypervisor as soon as the feature was ratified by the NVMe working group, even before it was publicly released.

There were very few changes from the original proposal, I.e. opcodes, return values and now fancy names; the buffers (as described in my last post) are now called Shadow Doorbell and EventIdx buffers.

In short, the first one mimics the Doorbell registers in memory, allowing the emulated controller to fetch the Doorbell value when convenient instead of waiting for the Doorbell register to be written. For its part, the EventIdx provides a hint given by the emulated controller to tell the host if the Doorbell register needs to be updated (in case the emulated controller is not fetching the Doorbell value from the Shadow Doorbell buffer). You can check section 7.13 of the specification for an example of usage.

Results

The following test results were obtained in a machine of type n1-standard-4 (4 vCPUs, 15 GB memory) at Google Cloud Engine platform with Kernel 4.12.0-rc5 using the following command:

$ sudo fio --time_based --name=benchmark --runtime=30 \ --filename=/dev/nvme0n1 --nrfiles=1 --ioengine=libaio --iodepth=32 \ --direct=1 --invalidate=1 --verify=0 --verify_fatal=0 --numjobs=1 \ --rw=randread --blocksize=4k --randrepeat=0

Results (in Input/Ouput Operations per Second):
Without Shadow Doorbell and EventIdx buffers: 43.9K IOPS
With Shadow Doorbell and EventIdx buffers: 184K IOPS
Gain ~= 4 times

Screenshot - Without Shadow Doorbell and EventIdx buffers


Screenshot - With Shadow Doorbell and EventIdx buffers


Enjoy your enhanced numbers of IOPS! :D

 

Original post

Comments (0)


Add a Comment






Allowed tags: <b><i><br>Add a new comment:


Search the newsroom

Latest Blog Posts

Adding VP9 and MPEG2 stateless support in v4l2codecs for GStreamer

23/06/2021

Earlier this year, from January to April 2021, I worked on adding support for stateless decoders for GStreamer as part of a multimedia internship…

Bag of Freebies for XR Hand Tracking: Machine Learning & OpenXR

17/06/2021

In our previous post, we presented a project backed by INVEST-AI which introduces a multi-stage neural network-based solution. Now let's…

Testing cameras with lc-compliance on KernelCI

15/06/2021

Initiated as a joint effort by the Google Chrome OS team and Collabora, the recent KernelCI hackfest brought the addition of new tests including…

Zink: Summer 2021 update

14/06/2021

There's a lot that has happened in the world of Zink since my last update, so let's see if I can bring you up to date on the most important…

Open Source OpenGL ES 3.1 on Mali GPUs with Panfrost

11/06/2021

Panfrost, the open source driver for Arm Mali, now supports OpenGL ES 3.1 on both Midgard (Mali T760 and newer) and Bifrost (Mali G31, G52,…

Optimizing 3D performance with virglrenderer

17/05/2021

Collabora has been investing into Perfetto to enable driver authors & users to get deep insights into driver internals and GPU performance.…

Open Since 2005 logo

We use cookies on this website to ensure that you get the best experience. By continuing to use this website you are consenting to the use of these cookies. To find out more please follow this link.

Collabora Ltd © 2005-2021. All rights reserved. Privacy Notice. Sitemap.

Collabora Limited is registered in England and Wales. Company Registration number: 5513718. Registered office: The Platinum Building, St John's Innovation Park, Cambridge, CB4 0DS, United Kingdom. VAT number: 874 1630 19.