[VM] NCM performance report

shaping at bigfoot.com shaping at bigfoot.com
Tue Apr 6 14:07:17 UTC 1999


----- Original Message -----
From: Peter Crowther <peter.crowther at it-iq.com>
To: <squeak at cs.uiuc.edu>
Sent: Tuesday, April 06, 1999 5:08 AM
Subject: RE: [VM] NCM performance report


> > From: Dan Ingalls [mailto:DanI at wdi.disney.com]
> > Sent: 25 March 1999 06:15
> [...]
> > We have been considering
> > th NCM changes since Tim first got them working.  Simplicity
> > and malleability are certainly positive features.
> > Performance, if it's real, is as well.
> >
> > The main reason I have balked at this change so far is the
> > cost in space for small implementations
> [...]
> > A competing change we have been weighing for a long time is
> > to do away with compact headers.  This would add about the
> > same amount of space (70k) to the mini image, but would yield
> > greater simplifications and speedups in the virtual machine
> > (IMO).
>
> [I know, I'm late as usual.  I've been off-site for a couple of weeks and,
> while I could get at my mailbox, I couldn't mail out]
>
> For interest, I tried bodging the SystemTracer to write out an image with
> 3-word headers for every object in the distribution 2.3 image.  It took a
> 3.5Mb image to a shade over 5Mb if I made the correct changes --- a large
> penalty on a PDA.  The flip side is that some of us [hi Adrian] trying to
> run multi-user systems on Squeak are willing to pay that space for a large
> speedup if we could get one.

I am, too.

  I've had my head in the object allocation and
> GC stuff, so may have a biased view, but it looks like some considerable
> speed could be gained by doing away with the twisty turny maze of tests
> about object formats.  Has anyone done any experiments in this area?  If
> not, it looks like I'll have to do this anyway at some point, as adding an
> optional fourth security word to the header causes all kinds of merry hell
> if you try to keep the existing variable-length headers.

Simplify.


Cheers.





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