[Vm-dev] how slower is called a named primitive over a numbered primitive?

[Eliot Miranda]

Hi Esteban,

    you can set up a test using the LargeInteger comparison primitives.
They're both named and numberd.  e.g.

23 primitiveLessThanLargeIntegers

So you can write e.g.

LargePositiveInteger>>#< anInteger
"Primitive. Compare the receiver with the argument and answer true if
the receiver is less than the argument. Otherwise answer false. Fail if the
argument is not a SmallInteger or a LargePositiveInteger less than
2-to-the-30th (1073741824).
Optional. See Object documentation whatIsAPrimitive."

<primitive: 23>
^super < anInteger

as

numberedLessThan: anInteger
"Primitive. Compare the receiver with the argument and answer true if
the receiver is less than the argument. Otherwise answer false. Fail if the
argument is not a SmallInteger or a LargePositiveInteger less than
2-to-the-30th (1073741824).
Optional. See Object documentation whatIsAPrimitive."

<primitive: 23>
^super < anInteger


namedLessThan: anInteger
"Primitive. Compare the receiver with the argument and answer true if
the receiver is less than the argument. Otherwise answer false. Fail if the
argument is not a SmallInteger or a LargePositiveInteger less than
2-to-the-30th (1073741824).
Optional. See Object documentation whatIsAPrimitive."

<primitive: 'primitiveLessThanLargeIntegers'>
^super < anInteger

and test it with two suitable large integers.  Will you report back?  I'd
like to know the answer.  Named primitive invocation should be slightly
slower.  As Clément says, a return different address is written to the
stack, overwriting the primitive code, but that return path is essentially
the same as for numbered primtiives.  So I expect that there will be almost
no measurable difference.

This is all to do with callbacks.  Numbered primitives are assumed never to
callback (so far that's a valid assumption).  But named primitives (such as
an FFI call) may indeed callback and hence, by the time the primitive
finally returns the code zone may have been compacted and the original
method containing the callout may have moved.  So the VM can't simply
return to a primitive that may have called back, and then have that
primitive's code return form the primitive, because that codee may have
moved.  The solution is to provide a piece of code at a fixed address that
returns from a named primitive call, and have the return sequence run that
code.

On Mon, Jun 22, 2015 at 5:13 AM, Esteban Lorenzano <estebanlm at gmail.com>
wrote:

>
> Hi,
>
> Any idea how slower is? I mean, any measure/estimation/something around?
>
> cheers,
> Esteban
>
>


-- 
best,
Eliot
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