Re: [PATCH, v10 3/3] cgroups: introduce timer slack controller

Matthew Garrett
2011-10-17T15:00:08Z

On Mon, Oct 17, 2011 at 04:49:29PM +0200, Peter Zijlstra wrote:
> On Mon, 2011-10-17 at 15:40 +0100, Matthew Garrett wrote:
> > On Mon, Oct 17, 2011 at 04:28:27PM +0200, Peter Zijlstra wrote:
> > > An XDamage and repaint from the X client, after which your copy will
> > > complete and you get what you asked for?
> >
> > An XDamage and then an asynchronous RPC call to the remote server to
> > identify the contents of the next frame before drawing them, plus some
> > sort of new synchronisation mechanism for blocking the X query until
> > that point?
>
> Why would this be a problem?
>
> I mean, why would getting a copy of an otherwise invisible surface be a
> performance sensitive path? If the compositor needs the surface it would
> make it visible and send the XDamage once and keep it visible henceforth
> until the time it again becomes invisible, at which point you have to
> stop updates again.

I'm not saying that it's a problem. I'm saying that your approach
changes behavioural semantics in a way that may violate application
expectations just as surely as changing the timer behaviour does.
There's no free approach.

> > Timers are a resource. People want to manage that resource. cgroups are
> > a convenient mechanism for managing resources.
>
> Yes, and a ball is round (unless you're a USA-ian, in which case they're
> ovoid), what's your point?

If there's no reason to want to manage that resource, why do we support
timer slack at all?

--
Matthew Garrett | mjg59@srcf.ucam.org