[Vm-dev] [Pharo-project] Plan/discussion/communication around new object format

stephane ducasse stephane.ducasse at gmail.com
Fri Jun 15 19:15:49 UTC 2012

Hi dave

I asked camillo to do that a week ago on a similar topics. So we will see.


On Jun 15, 2012, at 2:49 AM, David T. Lewis wrote:

> On Fri, Jun 15, 2012 at 01:15:15AM +0200, Igor Stasenko wrote:
>> On 14 June 2012 23:44, Eliot Miranda <eliot.miranda at gmail.com> wrote:
>>> But so you know what the performance overhead is? ??In VisualWorks it was < 5% over a wide range of benchmarks (e.g. real benchmarks such as recompile the system).
>> Yes i remember this number.
>> But, lets pose the *right* question:
>> - guys we have extra 5% of performance to waste,
>> what feature you would like to spend it on?
> It seems to me that some of the topics being discussed here might benefit
> from empirical measurements. For example, a particular object header format
> might have an effect on the speed of walking through the object memory heap.
> In such a case, it would be relatively easy to take measurements to estimate
> the actual performance that might be expected without actually doing a complete
> implementation. The process might look something like this:
> - Trace an image to the desired new format. Do not worry about making it
> functional, just make it good enough that objects in the traced image can
> be reached with #objectAfter:
> - Hack the interpreter code just enough to make #objectAfter: work with the
> new object format. Do not worry about making a functional VM.
> - Generate a new "VM" that gets just far enough to load the image into an
> object memory. Turn off inlining when generating the "VM" so that a profiler
> can see where the time is being spent. Arrange for the "VM" to go immediately
> into a loop that walks through the object memory from firstAccessibleObject
> to end of memory (see StackInterpreter>>allAccessibleObjectsOkay for example).
> Loop for a few thousand iterations through the heap, then exit.
> - Profile it (gprof). See where the time goes and how long it takes to run
> to completion.
> - Compare the results obtained with various object header strategies.
> Experiments like this might produce some very useful insights. It would be a
> lot of work for one person to do all the research on this, but it seems to me
> that we now have quite a few interested and competent VM hackers who might be
> willing to pitch in to obtain empirical data.
> Any interest?
> Dave

More information about the Vm-dev mailing list