Re: [PATCH] MMIO: Make coalesced mmio use a device per zone

[Avi Kivity <avi@redhat.com>]

On 07/19/2011 08:23 PM, Jan Kiszka wrote:
> On 2011-07-19 19:17, Avi Kivity wrote:
> >  On 07/19/2011 08:14 PM, Jan Kiszka wrote:
> >>
> >>  Another improvement - unfortunately less transparent for user space -
> >>  would be to overcome the single ring buffer that forces us to hold a
> >>  central lock in user space while processing the entries. We rather need
> >>  per-device rings. While waiting for coalesced VGA MMIO being processed,
> >>  way too many kittens are killed.
> >>
> >>  I have this on our agenda, but I wouldn't be disappointed as well if
> >>  someone else is faster.
> >
> >  The socket mmio would have accomplished this as well.
>
> I haven't followed the outcome in all details - is that approach dead
> due to its complexity?
>
> >  One thing to
> >  beware of is to preserve correctness:
> >
> >  1) write to 0xa0000 (queued)
> >  2) write to 0xa0002 (queued)
> >  3) remap 0xa0000 region (executed)
>
> Obviously, there must be 3a) here: drain all affected queues.

How do you implement this 3a, if your consumers are outside the main 
process?  I guess you could have an additional synchonize API (for 
in-kernel consumers) or RPC (for external process consumers), but then 
this is no longer a simple API.

> >  4) write to 0xa000 (queued)
> >  5) drain queue
> >
> >  writes 1 and 2 go to the wrong place.
> >

-- 
error compiling committee.c: too many arguments to function