[PATCH v2 weston 00/16] Atomic modesetting support

[Pekka Paalanen]

On Fri, 26 Jun 2015 14:27:48 +0100
Daniel Stone <daniel at fooishbar.org> wrote:

> Hi,
> 
> On 24 June 2015 at 13:11, Pekka Paalanen <ppaalanen at gmail.com> wrote:

> > I think the best way to cache state is to let it stay in the kernel,
> > and avoid submitting a disable followed by the old state that's already
> > there. If we manage that, maintaining cached atomic req pieces in
> > weston would be moot.
> 
> Can you expand a bit on what you mean here?

Gaining anything from a req snippet cache depends on the need to submit
already submitted state again. The only significant reason to do that,
that I can imagine, would be if the algorithm unconditionally
initialized the req with either that cached state or disabled state.

If we avoid unconditionally initializing a req like that, I don't see
what we would gain from a req snippet cache. And we can avoid it,
because the kernel maintain all state we do not set.

I assume the cases where we need to re-program all state are rare
enough to not warrant this added code.

Therefore, if we only program state that has changed, the cache would
be a net cost rather than a win, as we'd (almost) never hit the cache.


Thanks,
pq