Re: [RFC] /dev/ioasid uAPI proposal

From: Jason Gunthorpe
Date: Wed Jun 02 2021 - 13:22:11 EST

On Wed, Jun 02, 2021 at 04:54:26PM +0800, Jason Wang wrote:
> 在 2021/6/2 上午1:31, Jason Gunthorpe 写道:
> > On Tue, Jun 01, 2021 at 04:47:15PM +0800, Jason Wang wrote:
> > > We can open up to ~0U file descriptors, I don't see why we need to restrict
> > > it in uAPI.
> > There are significant problems with such large file descriptor
> > tables. High FD numbers man things like select don't work at all
> > anymore and IIRC there are more complications.
> I don't see how much difference for IOASID and other type of fds. People can
> choose to use poll or epoll.

Not really, once one thing in an applicate uses a large number FDs the
entire application is effected. If any open() can return 'very big
number' then nothing in the process is allowed to ever use select.

It is not a trivial thing to ask for

> And with the current proposal, (assuming there's a N:1 ioasid to ioasid). I
> wonder how select can work for the specific ioasid.

pagefault events are one thing that comes to mind. Bundling them all
together into a single ring buffer is going to be necessary. Multifds
just complicate this too