[LSF/MM/BFP ATTEND] [LSF/MM/BFP TOPIC] Storage: Copy Offload

[Nitesh Shetty <nj.shetty@samsung.com>]

Hi all,

Background:
===========
Copy offload is a feature that allows file-systems or storage devices
to be instructed to copy files/logical blocks without requiring
involvement of the local CPU.
We are working on copy offload[1], mainly focused on NVMe Copy command
(single NS, TP 4065) and NVMe over fabrics.
Previously Chaitanya Kulkarni presented talk on copy offload[2].

Current state of work:
======================
	Our latest patch series[1] covers
	1. Driver
		- NVMe Copy command (single NS, TP 4065), including support
		in nvme-target (for block and file back-end).

	2. Block layer
		- Block-generic copy (REQ_COPY flag), with interface
		accommodating two block-devs, and multi-source/destination
		interface
		- Emulation, when offload is natively absent
		- dm-linear support (for cases not requiring split)

	3. User-interface
		- new ioctl

	4. In-kernel user
		- dm-kcopyd
		
	5. Tools:
		- fio
		- blktests

	Performance:
	With the async design of copy-emulation/offload using fio[3],
	we were  able to see the following improvements as
	compared to userspace read and write on a NVMeOF TCP setup:
	Setup1: Network Speed: 1000Mb/s
		Host PC: Intel(R) Core(TM) i7-8700 CPU @ 3.20GHz
		Target PC: AMD Ryzen 9 5900X 12-Core Processor
		block size 8k, range 1:
			635% improvement in IO BW (107 MiB/s to 787 MiB/s).
			Network utilisation drops from  97% to 14%.
		block-size 2M, range 16:
			2555% improvement in IO BW (100 MiB/s to 2655 MiB/s).
			Network utilisation drops from 89% to 0.62%.
	Setup2: Network Speed: 100Gb/s
		Server: Intel(R) Xeon(R) Gold 6240 CPU @ 2.60GHz, 72 cores
			(host and target have the same configuration)
		block-size 8k, range 1:
			6.5% improvement in IO BW (791 MiB/s to 843 MiB/s).
			Network utilisation drops from  6.75% to 0.14%.
		block-size 2M, range 16:
			15% improvement in IO BW (1027 MiB/s to 1183 MiB/s).
			Network utilisation drops from 8.42% to ~0%.
	Overall, in these tests, kernel copy emulation reduces network utilisation
	drastically and improves IO bandwidth.

What we will discuss in the proposed session ?
==============================================
Through this session I would like to discuss and get opinion of community
on minimum set of requirement for copy offload for this phase. Also share
some of the blockers we are facing and would get opinion on how we can
proceed further.

Required attendees:
===================
	Martin K. Petersen
	Jens Axboe
	Christoph Hellwig
	Mike Snitzer
	Hannes Reinecke
	Chaitanya Kulkarni
	Bart Van Assche
	Damien Le Moal
	Mikulas Patocka
	Keith Busch
	Sagi Grimberg
	Javier Gonzalez
	Kanchan Joshi

Links:
======
[1] https://lore.kernel.org/lkml/20230112115908.23662-1-nj.shetty@samsung.com/T/#m91a2f506eaa214035a8596fa9aa8d2b9f46654cc
[2] https://lore.kernel.org/all/BYAPR04MB49652C4B75E38F3716F3C06386539@BYAPR04MB4965.namprd04.prod.outlook.com/
[3] https://github.com/vincentkfu/fio/tree/copyoffload