Hi Christoph,

On Sat, Mar 07, 2020 at 06:11:56PM +0000, Thiede, Christoph wrote:
> Hi Dave, hi all,
> 
> 
> this sounds like a really interesting changeover. I have heard and
> read some rumors about Sista in the past, but I could not find any
> brief but complete summary of all the changes this will make to our
 existing Smalltalk system. So it would be great if you could point
> us to some kind of changelog.
> 

You can think of the bytecode set as the machine level instructions
that are executed by the virtual machine, analogous to the hardware
instructions that are executed by a CPU. Eliot has arranged for Squeak
(and Pharo and others) to be able to change over to an alternate
instruction set, sort of like changing the CPU on your computer without
turning the power off.

The motivation for the new bytcodes (called Sista) is to enable certain
kinds of performance optimizations directly in the image. Think in
terms of some of the performance optimizations in the Cog/Spur VMs,
but now potentially being able to do it directly in the image.

Others will have to give you the details, but that's the basic idea.

> 
> In what way will this affect your typical Squeak experience? What
> about performance? What about debugging/simulating code? As someone
> who did not yet deal with any VM side effects, I would be interested
> to hear about the practical effects you can see when playing around
> with Context & Compiler stuff. I read about FullBlockClosure which
> appears to be kind of detached of its defining method. How will this
> change accessing thisContext home etc. from a FullBlockClosure, for
> example? I read Sista stores an optimization cache between several
> runs. Where will this information be saved, at the image side or
> at the VM side?
> 

I cannot answer much of this, other than to say that initially you
should expect to see no difference in the user experience. Various
people have been using Sista for some time without problems, so it
will initially be a transparent change, with the more interesting
things happening in the future :-)

Dave


> Lots of questions, maybe someone can answer a few of them :-)
> 
> 
> Best,
> 
> Christoph
> 
> ________________________________
> Von: Squeak-dev <squeak-dev-bounces at lists.squeakfoundation.org> im Auftrag von David T. Lewis <lewis at mail.msen.com>
> Gesendet: Samstag, 7. M?rz 2020 18:29:40
> An: squeak-dev at lists.squeakfoundation.org
> Betreff: Re: [squeak-dev] Switching to Sista bytecodes in trunk (was: The Inbox: Kernel-dtl.1310.mcz)
> 
> I will leave this in the inbox for a couple of days, and if there are
> no objections I will move it to trunk.
> 
> Dave
> 
> On Fri, Mar 06, 2020 at 07:43:29PM -0500, David T. Lewis wrote:
> > The Sista bytecode set enables important reasearch and development work.
> > Eliot and Clemont can explain better than me (apologies to Clemont Bera
> > for using my seven-bit character set on your name).
> >
> > Squeak 5.3 is released and we are starting the new release cycle, so it
> > is time to make Sista the default in trunk. Kernel-dtl.1310 (in the inbox)
> > activates Sista in the package postscipt.
> >
> > Dave
> >
> > On Sat, Mar 07, 2020 at 12:29:13AM +0000, commits at source.squeak.org wrote:
> > > David T. Lewis uploaded a new version of Kernel to project The Inbox:
> > > http://source.squeak.org/inbox/Kernel-dtl.1310.mcz
> > >