Re: Ummunotify: progress at last!

[Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>]

On Wed, Apr 07, 2010 at 12:37:03PM -0700, Roland Dreier wrote:
>  > No, there is no mmap. Like this:
>  > 
>  > u64 my_counter = 0;
>  > 
>  > ibv_set_mmu_counter(verbs, &my_counter);
>  > [..]
>  > while (my_counter != last_my_counter) {
>  >     last_my_counter = my_counter;
>  >     ibv_get_mmu_notifications(verbs, ...);   // <- I am a memory barrier as well
>  > }
>  > 
>  > The kernel 'syscall' ibv_set_mmu_counter would bind the given verbs to
>  > the 8 byte counter you specified without having to the mmap thing. As
>  > I understand it this is what perfevents does.
> 
> I was trying to look at how perf events handles this, and AFAICT it
> looks like kernel/perf_event.c just supports mmap().  Can you expand on
> what you meant here?
> 
> (I was trying to figure out how one would handle the case where
> userspace gives us a counter in highmem -- doing kmap_atomic() seems to
> be to only option but then I'm not sure if I want to deal with that...)

I think I was mistaken here, disregard..

Jason
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