2010/11/13 Levente Uzonyi leves@elte.hu:
On Sat, 13 Nov 2010, Igor Stasenko wrote:
On 12 November 2010 17:44, Bert Freudenberg bert@freudenbergs.de wrote:
On 12.11.2010, at 14:41, Igor Stasenko wrote:
I'm inviting you to make own version of benchmark
I don't think this can be realistically simulated inside Squeak. But possibly you could change the macros in sqMemoryAccess.h to fake an object table access?
I just tried that. Using tinyBenchmarks, byte code performance drops to 63% and sends to 78%.
Now declaring that variable volatile might be overkill as it prevents all caching, but I couldn't quite figure out a more realistic declaration.
you mean that non-volatile like:
int FakeObjTable = 0;
could be optimized away by compiler? Well, since compiler compiles module by module (a separate C files), if you remove 'static' it can no longer able to optimize it to no-op, since it can't guess what may happen to this variable in another object file, since even if in one module there only a read-only access to it, some other module could contain a code which modifying it.
So, i think this is the worst case performance slowdown. :)
If we take into account that to get object location you need to do object table look only once, and then any consequent read/write operations on object won't require table lookup, this can be improved.
You can't do that if you want O(1) time for #become:.
Can you elaborate? For instance, lets take a bytecode read. Should each bytecode read also go through object table?
Levente
Consider, for example, that to read ivar, interpreter reads & checks header, and only then ivar slot, so it should cost: 1 table lookup and 2 reads at object location. instead of 2 table lookups + 2 reads at object location.
- Bert -