Re: [RFC 08/16] vfio/type1: Cache locked_vm to ease mmap_lock contention

[Jason Gunthorpe]

On Thu, Jan 06, 2022 at 10:06:42PM -0500, Daniel Jordan wrote:

> > At least it seems like it is not an insurmountable problem if it makes
> > an appreciable difference..
> 
> Ok, I can think more about this.

Unfortunately iommufd is not quite ready yet, otherwise I might
suggest just focus on that not type 1 optimizations. Depends on your
timeframe I suppose.

> > After seeing Daniels's patches I've been wondering if the pin step in
> > iommufd's draft could be parallized on a per-map basis without too
> > much trouble. It might give Daniel a way to do a quick approach
> > comparison..
> 
> Sorry, comparison between what?  I can take a look at iommufd tomorrow
> though and see if your comment makes more sense.

I think it might be easier to change the iommufd locking than the
type1 locking to allow kernel-side parallel map ioctls. It is already
almost properly locked for this right now, just the iopt lock covers a
little bit too much.

It could give some idea what kind of performance user managed
concurrency gives vs kernel auto threading.

Jason