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

[Daniel Jordan]

On Fri, Jan 07, 2022 at 11:18:07AM -0400, Jason Gunthorpe wrote:
> 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.

Ok, I see.  Well, sooner the better I guess, we've been carrying changes
for this a while.

> > > 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.

Aha, I see, thanks!