Thanks A LOT for your effort!!!
Stef
On May 22, 2011, at 5:54 PM, David T. Lewis wrote:
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