[Intel-gfx] [RFC 4/4] drm: add support for raw monotonic vblank timestamps

[Michel Dänzer]

On Fre, 2012-10-05 at 16:59 +0300, Imre Deak wrote: 
> On Fri, 2012-10-05 at 15:55 +0200, Michel Dänzer wrote:
> > On Fre, 2012-10-05 at 16:37 +0300, Imre Deak wrote: 
> > > In practice we never want the timestamps for vblank and page flip events
> > > to be affected by time adjustments, so in addition to the gettimeofday
> > > timestamps we used so far add support for raw monotonic timestamps.
> > > 
> > > For backward compatibility use flags to select between the old and new
> > > timestamp format.
> > > 
> > > Note that with this change we will save the timestamp in both formats,
> > > for cases where multiple clients are expecting an event notification in
> > > different time formats.
> > 
> > I wonder if all this trouble is really necessary. I honestly can't
> > imagine any user of this API requiring non-monotonic timestamps and
> > breaking with monotonic ones. I think it was simply a mistake that we
> > didn't make them monotonic in the first place (or maybe it wasn't even
> > possible when this API was first introduced).
> 
> Yea, I'd rather simply switch over to monotonic timestamps too. But that
> would break apps that already compare against the wall time for whatever
> purpose (for example A/V sync).

Are there actually any such apps in the real world? Do they work when
the wall time jumps?


-- 
Earthling Michel Dänzer           |                   http://www.amd.com
Libre software enthusiast         |          Debian, X and DRI developer