Request for review (L): 7087838: JSR 292: add throttling logic for optimistic call site optimizations

[Rémi Forax]

On 09/18/2011 07:16 PM, Mark Roos wrote:
> In looking at my code.
>
> In general 98% of the callsites are < 3 targets.
>
> Those that are larger I can catch and use a different lookup.  I also 
> believe that Charles Nutter limits his
> depth to 5.
>
> So the general case I see will not exceed the < 10.
>
> But I do have some cases where 10 is not the right number
>
>         Part of my app is a compiler so some of its callsites see 20 
> or 30 classes ( AST node types).
>         And part is a data flow evaluator where the data has about 30 
> types

For these callsites you should use a dispatch table (a vtable dedicated 
to a callsite)
instead of a sequence of 20 guards, because your code is equivalent to 
looking up
a class in a linkedlist, so it's awfully slow.
Moreover, are you sure the code that contains these callsites is JITed,
it's pretty easy to hit other thresholds like by example
the max number of internal nodes (ideal nodes).

>
> And as I watch the jit work it attacks these sites pretty fast so I 
> could image exceeding the > 10.
>
> I would like both or these to jit as they are used a lot
>
> And my final use case which is dynamic method replacement.  Here I 
> have to reset the callsites so they
> get the correct code.  In our system this happens doing feature 
> loading ( small dynamic patches) and for
> changing math operations ( dataflow) and finally during edit.  Both 
> easily exceed the >10 during the execution
> life of the app (hopefully months).
>
> I would be fine if there was a way to tell the jitter to reset its 
> counts on a callsite as all of my use cases
> can absorb time at that instance.  I really would have issues with 
> losing the jitting when the app is expected
> to be running at full speed and would have to find some clever hack 
> around it.
>
> Another point is that the classes callsites see during startup can be 
> quite different than during normal operation.
> This is another reason we do the bulk invalidation
>
> mark

Rémi

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