[racket-dev] gc vs assignment

On Wed, 2010-08-25 at 08:33 -0600, Jay McCarthy wrote:
> On Tue, Aug 24, 2010 at 3:47 PM, Neil Toronto <neil.toronto at gmail.com> wrote:
> > Matthias Felleisen wrote:
> >>
> >> Catching up with some mail.
> >> Neil wrote:
> >>>
> >>> Avoiding allocation reduces GC collects, which reduces stutters and
> >>> hitches.
> >>
> >> My (possibly old) understanding of GC and mutation tell me that this
> >> is one of those prejudices that programmers should get rid of. Every
> >> mutation goes across an access barrier in a GC like ours and can thus
> >> be much more expensive than a lightweight allocation. This was
> >> certainly true for early generational collectors. I do know that the
> >> hordes of Java programmers who invaded GCLand forced GC builders to
> >> make C/C++-like programs in Java work reasonably fast with collectors
> >> and so collectors changed.
> >
> > In my defense, I was talking about framerate, not total or average cost of
> > memory management. A GC pause in my game test app lasts 50ms to 200ms, which
> > causes a "hitch": a noticeable, temporary drop in framerate and
> > responsiveness, in this case down to 20Hz to 5Hz. For comparison, 60Hz is an
> > ideal minimum. A sequence of minor hitches is a stutter; sometimes Racket's
> > GC pause causes those as well.
> >
> > Inflicting hitches on users in a twitch game is a cardinal sin. In
> > non-twitch games they are eye-wrenching, especially when everything else is
> > smooth. Games are really almost real-time apps.
> 
> Totally disagree. Here's a crazy forum where you will find people
> complaining about how a recent release (DeathSmiles - North America
> for Xbox360) is garbage because there isn't ENOUGH slowdown as
> compared to the Japanese 360 or XBox release:
> 
> http://www.aksysgames.com/forums/topic/732

Doesn't this article just say that the game is running too fast? Maybe
the American version doesn't stutter, but the game developers should
have put in better speed control rather than depending on a slow
machine/implementation.  I'd like to say this doesn't count as a counter
example.

But let's just say that in 99.9% of games it is a sin to stutter, though
not in all of them.

-Everett

> 
> I do agree that you personally don't want a drop in frame rate and
> that the GC gets in your way of achieving that goal.
> 
> Jay
> 
> >
> > I'm still doing the game universe-style, so I haven't moved to mutation yet.
> > I'm halfheartedly considering it. I'll probably try an allocation pool of
> > same/similar-sized arrays first. I'd gladly pay half of my ideal 16ms per
> > frame to eliminate hitches.
> >
> > Neil T
> >
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> >
> 
> 
> 
> -- 
> Jay McCarthy <jay at cs.byu.edu>
> Assistant Professor / Brigham Young University
> http://teammccarthy.org/jay
> 
> "The glory of God is Intelligence" - D&C 93
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