On 07.12.2020 15:56, Hannes Reinecke wrote:
On 12/7/20 3:11 PM, Christoph Hellwig wrote:
So, I'm really worried about:
a) a good use case. GC in f2fs or btrfs seem like good use cases, as
does accelating dm-kcopyd. I agree with Damien that lifting dm-kcopyd
to common code would also be really nice. I'm not 100% sure it should
be a requirement, but it sure would be nice to have
I don't think just adding an ioctl is enough of a use case for complex
kernel infrastructure.
b) We had a bunch of different attempts at SCSI XCOPY support form IIRC
Martin, Bart and Mikulas. I think we need to pull them into this
discussion, and make sure whatever we do covers the SCSI needs.
And we shouldn't forget that the main issue which killed all previous
implementations was a missing QoS guarantee.
It's nice to have simply copy, but if the implementation is _slower_
than doing it by hand from the OS there is very little point in even
attempting to do so.
I can't see any provisions for that in the TPAR, leading me to the
assumption that NVMe simple copy will suffer from the same issue.
So if we can't address this I guess this attempt will fail, too.
Good point. We can share some performance data on how Simple Copy scales
in terms of bw / latency and the CPU usage. Do you have anything else in
mind?
