Re: [PATCH] evdev: flush ABS_* events during EVIOCGABS

[Peter Hutterer <peter.hutterer@who-t.net>]

On Tue, Apr 22, 2014 at 11:07:47PM -0700, Dmitry Torokhov wrote:
> On Wed, Apr 23, 2014 at 03:55:28PM +1000, Peter Hutterer wrote:
> > On Tue, Apr 22, 2014 at 10:46:47PM -0700, Dmitry Torokhov wrote:
> > > On Wed, Apr 23, 2014 at 03:38:49PM +1000, Peter Hutterer wrote:
> > > > On Wed, Apr 23, 2014 at 10:21:03AM +1000, Peter Hutterer wrote:
> > > > > On Tue, Apr 22, 2014 at 08:21:54AM +0200, David Herrmann wrote:

..

> > > > 
> > > > any comments?
> > > 
> > > Do we really need to optimize the case when we are dropping events?
> > 
> > It happens frequently, to the point where on some laptops you're pretty much
> > guaranteed to get SYN_DROPPED events on resume and sometimes even during
> > normal multi-finger user.
> > 
> > I don't have any measurements on how many events are dropped on average.
> > Could be one or two, could be several buffer sizes, I honestly don't know.
> 
> I think we need to figure this out. The idea is that dropping events
> should be an exception, not a rule.

increase the buffer size for the devices I guess, with some heuristics
maybe. you could dynamically grow the buffer in the kernel, if the buffer
gets full or close to full, grow it.

but really, this is a moving target, eventually you will get the
SYN_DROPPED. if a client sleeps for a second or more, the events from a
second ago are likely useless anyway, so the need for an atomic sync exists
regardless. fwiw, I can live with a atomic sync that clears the client
buffer provided I get the correct state. any optimisation on top of that can
be done afterwards.

Cheers,
   Peter