Improving next_buffer() rpc

Gerry Boland gerry.boland at
Thu Jul 10 10:01:22 UTC 2014

On 09/07/14 16:39, Kevin Gunn wrote:
> First
> Not sure we're still on topic necessarily wrt changing from id's to fd's
> do we need to conflate that with the double/triple buffering topic ?
> let's answer this first...
> Second
> while we're at it :) triple buffering isn't always a win. In the case of
> small, frequent renders (as an example "8x8 pixel square follow my finger")
> you'll have potentially 2 extra buffers that need their 16ms of fame on the
> screen in the queue, 1 at session server, 1 at system server. Which can
> look a little laggy. I'm willing to say in the same breath though, that
> this may be lunatic fringe. The win for the triple buffering case is likely
> more common, which is spikey render times (14+ms) amongst more normal
> render times (9-12ms)
> +1 on giving empty buffers back to the clients to allow them to have a
> "queue" of empty buffers at their disposal (i'm not sure if RAOF is correct
> or duflu in that its "synchronously waiting for a round trip every swap"...can
> we already have an empty buffer queue on the client side ?)

I also want to remind everyone that our default shipping configuration
is a root mir server with a nested mir server as a client, and that
nested mir server manages most client apps the user will be interacting

Nesting will increase input latency, as now there's not just 3 buffers
in play, but more (5 yeah?).

I had thought that the double-buffering idea was to try reduce the
number of buffers being used in the nested case. Sounds like Daniel
isn't confident that'll work now, which is a pity.

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