From: Dan Ingalls [mailto:DanI@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'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.
All thoughts welcome!
- Peter