Hi Pavel,
Good job on the io_uring zerocopy stuff, that looks really interesting!
I'm working on adding a new userspace/kernelspace buffer interface for
the IIO subsystem. My first idea (a few years ago already) was to add
support for splice(), so that the data could be sent from IIO hardware
directly to file or to the network.
It turned out not working really well because of how splice() works.
The kernel would erase pages to be exchanged with the pipe data pages,
so the speed gains obtained by not copying data pages were
underwhelming and the CPU usage was almost as high (CPU usage being our
limiting factor here).
We then settled for a dmabuf-based interface [1] which works great as a
userspace/kernelspace interface, but doesn't allow zero-copy to disk or
network (until someone adds support for it, I guess). The patchset got
refused on the basis that (against all documentation) dmabuf really is
a gpu/drm thing and shouldn't be used elsewhere.
My question for you is, would your new io_uring zerocopy work allow for
instance to transfer data from storage to the network, without
triggering this "page clearing" mechanism that splice() has?
Cheers!
-Paul
[1]
https://lore.kernel.org/linux-doc/20220207125933.81634-7-paul@xxxxxxxxxxxxxxx/T/
