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From: Bart Van Assche <bvanassche@acm.org>
To: Selva Jove <selvajove@gmail.com>, ksummit@lists.linux.dev
Cc: joshiiitr@gmail.com, nitheshshetty@gmail.com
Subject: Re: [TECH TOPIC] Settling Copy Offload via NVMe SCC
Date: Fri, 25 Jun 2021 09:02:51 -0700	[thread overview]
Message-ID: <effe01f3-ddf9-64f8-da96-61bb82bfabc9@acm.org> (raw)
In-Reply-To: <CAHqX9vZ_F4p0J_E3DZ4eoW0d3J2dZET5GEbM4Gr5wkUdRRPsAQ@mail.gmail.com>

On 6/25/21 7:47 AM, Selva Jove wrote:
> The de-facto way of copying data in I/O stack has been pulling it from
> one location followed by pushing to another. The farther the
> application, requiring copy, is from storage, the longer it takes for
> the trip to be over. With copy-offload the trips get shorter as the
> storage device presents an interface to do internal data-copying. This
> enables the host to optimise the pull-and-push method, freeing up the
> host CPU, RAM and the fabric elements.
> 
> The copy-offload interface has existed in SCSI storage for at least a
> decade through XCOPY but faced insurmountable challenges in getting
> into the Linux I/O stack. As for NVMe storage, copy-offload made its
> way into the main specification with a new Simple Copy Command(SCC)
> recently. This has stimulated a renewed interest and efforts towards
> copy-offload in the Linux community.
> 
> In this talk, we speak of the upstream efforts that we are doing around SCC -
> https://lore.kernel.org/linux-nvme/20210219124517.79359-1-selvakuma.s1@samsung.com/#r
> 
> We'd extensively cover the design-decisions and seek the feedback on
> the plumbing aspects such as -
> 
> 1. User-interface. Should it be a new ioctl/syscall, io_uring based
> opcode or must it fit into existing syscalls such as copy_file_range.
> 2. The transport mode between block-layer and NVMe. A chain of empty
> bios (like discard) vs bio with payload.
> 3. Must SCSI XCOPY compatibility be considered while we go about
> building interfaces around NVMe SCC?
> 4. Feasibility and challenges for in-kernel use cases, including the
> file-systems and device-mappers

This topic seems closely related to "Storage: Copy Offload"
(https://lore.kernel.org/linux-block/BYAPR04MB49652C4B75E38F3716F3C06386539@BYAPR04MB4965.namprd04.prod.outlook.com/).

Notes about implementing copy offloading are available at
https://github.com/bvanassche/linux-kernel-copy-offload.

Thanks,

Bart.

  reply	other threads:[~2021-06-25 16:02 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-25 14:47 Selva Jove
2021-06-25 16:02 ` Bart Van Assche [this message]
2021-06-25 16:08   ` James Bottomley
2021-06-29 14:40     ` Selva Jove

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