[Vm-dev] Performance of primitiveFailFor: and use of primFailCode
David T. Lewis
lewis at mail.msen.com
Sun May 22 15:54:18 UTC 2011
I have been trying to gradually update trunk VMMaker to better align
with oscog VMMaker (an admittedly slow process, but hopefully still
worthwhile). I have gotten the interpreter primitives moved into class
InterpreterPrimitives and verified no changes to generated code. This
greatly reduces the clutter in class Interpreter, so it's a nice change
I think.
My next step was to update all of the primitives to use the #primitiveFailFor:
idiom, in which the successFlag variable is replaced with primFailCode
(integer value, 0 for success, 1, 2, 3... for failure codes). This would
get us closer to the point where the standard interpreter and stack/cog
would use a common set of primitives. A lot of changes were required for
this, but the resulting VM works fine ... except for performance.
On a standard interpreter, use of primFailCode seems to result in a
nearly 12% reduction in bytecode performance as measured by tinyBenchmarks:
Standard interpreter (using successFlag):
0 tinyBenchmarks. '439108061 bytecodes/sec; 15264622 sends/sec'
0 tinyBenchmarks. '433164128 bytecodes/sec; 14740358 sends/sec'
0 tinyBenchmarks. '445993031 bytecodes/sec; 15040691 sends/sec'
0 tinyBenchmarks. '440999138 bytecodes/sec; 15052960 sends/sec'
0 tinyBenchmarks. '445993031 bytecodes/sec; 14485815 sends/sec'
After updating the standard interpreter (using primFailCode):
0 tinyBenchmarks. '393241167 bytecodes/sec; 14066256 sends/sec'
0 tinyBenchmarks. '392036753 bytecodes/sec; 15040691 sends/sec'
0 tinyBenchmarks. '393846153 bytecodes/sec; 14272953 sends/sec'
0 tinyBenchmarks. '400625978 bytecodes/sec; 14991818 sends/sec'
0 tinyBenchmarks. '393846153 bytecodes/sec; 15176750 sends/sec'
This is a much larger performance difference than I expected to see.
Actually I expected no measurable difference at all, and I was just
testing to verify this. But 12% is a lot, so I want to ask if I'm
missing something?
The changes to generated code generally take the form of:
Testing success status, original:
if (successFlag) { ... }
Testing success status, new:
if (foo->primFailCode == 0) { ... }
Setting failure status, original:
successFlag = 0;
Setting failure status, new:
if (foo->primFailCode == 0) {
foo->primFailCode = 1;
}
My approach to doing the updates was as follows:
- Replace all occurrences of "successFlag := true" with "self initPrimCall",
which initialize primFailCode to 0.
- Replace all "successFlag := false" with "self primitiveFail".
- Replace all "successFlag ifTrue: [] ifFalse: []" with
"self successful ifTrue: [] ifFalse: []".
- Update #primitiveFail, #failed and #success: to use primFailCode rather
than successFlag.
- Remove successFlag variable.
Obviously I don't want to publish the code on SqS/VMMaker, but I can mail
an interp.c if anyone wants to see the gory details (It is too large to
post on this mailing list though).
Any advice appreciated. I suspect I'm missing something basic here.
Thanks,
Dave
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