Re: Minutes from Feb 21 LSE Call

Kenneth Johansson
2003-02-24T01:16:51Z

On Mon, 2003-02-24 at 00:57, Alan Cox wrote:
> On Sun, 2003-02-23 at 20:50, Martin J. Bligh wrote:
> > >> And the baroque instruction encoding on the x86 is actually a _good_
> > >> thing: it's a rather dense encoding, which means that you win on icache.
> > >> It's a bit hard to decode, but who cares? Existing chips do well at
> > >> decoding, and thanks to the icache win they tend to perform better - and
> > >> they load faster too (which is important - you can make your CPU have
> > >> big caches, but _nothing_ saves you from the cold-cache costs).
> > >
> > > Next step: hardware gzip ?
> >
> > They did that already ... IBM were demonstrating such a thing a couple of
> > years ago. Don't see it helping with icache though, as it unpacks between
> > memory and the processory, IIRC.
>
> I saw the L2/L3 compressed cache thing, and I thought "doh!", and I watched and
> I've not seen it for a long time. What happened to it ?
>

http://www-3.ibm.com/chips/techlib/techlib.nsf/products/CodePack

If you are thinking of this it dose look like people was not using it I
know I'm not.It reduces memory for instructions but that is all and
memory is seems is not a problem at least not for instructions.

It dose not exist in new cpu's from IBM I don't know the official reason
for the removal.

If you really do mean compressed cache I don't think anybody has done
that for real.