On 04.12.2020 23:40, Keith Busch wrote:
On Fri, Dec 04, 2020 at 11:25:12AM +0000, Damien Le Moal wrote:On 2020/12/04 20:02, SelvaKumar S wrote: > This patchset tries to add support for TP4065a ("Simple Copy Command"), > v2020.05.04 ("Ratified") > > The Specification can be found in following link. > https://nvmexpress.org/wp-content/uploads/NVM-Express-1.4-Ratified-TPs-1.zip > > This is an RFC. Looking forward for any feedbacks or other alternate > designs for plumbing simple copy to IO stack. > > Simple copy command is a copy offloading operation and is used to copy > multiple contiguous ranges (source_ranges) of LBA's to a single destination > LBA within the device reducing traffic between host and device. > > This implementation accepts destination, no of sources and arrays of > source ranges from application and attach it as payload to the bio and > submits to the device. > > Following limits are added to queue limits and are exposed in sysfs > to userspace > - *max_copy_sectors* limits the sum of all source_range length > - *max_copy_nr_ranges* limits the number of source ranges > - *max_copy_range_sectors* limit the maximum number of sectors > that can constitute a single source range. Same comment as before. I think this is a good start, but for this to be really useful to users and kernel components alike, this really needs copy emulation for drives that do not have a native copy feature, similarly to what write zeros handling for instance: if the drive does not have a copy command (simple copy for NVMe or XCOPY for scsi), then the block layer should issue read/write commands to seamlessly execute the copy. Otherwise, this will only serve a small niche for users and will not be optimal for FS and DM drivers that could be simplified with a generic block layer copy functionality. This is my 10 cents though, others may differ about this.Yes, I agree that copy emulation support should be included with the hardware enabled solution.
Keith, Damien, Can we do the block layer emulation with this patchset and then work in follow-up patchses on (i) the FS interface with F2FS as a first user and (ii) other HW accelerations such as XCOPY? For XCOPY, I believe we need to have a separate discussion as much works is already done that we should align to.
