761618 - IonMonkey: Use IonMonkey only for hot scripts

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Jan de Mooij [:jandem]]

Currently JM and Ion use the same strategy to decide when a script is compiled:

1) Initial compilation after 40 calls and/or loop backedges.
2) Recompilation after 10,000 calls/backedges to inline calls.

These numbers make sense for JM because the alternative (interpreting) is very slow and compilation is pretty fast.

For Ion, the plan is to:

1) JM compilation after 40 calls/backedges.
2) Ion compilation after 10,000 calls/backedges, inlining calls.

The main benefit is that we don't waste time optimizing "warm", not hot, functions and this avoids some regressions, especially on SS.

I prototyped this change and the initial results are promising, SS/Kraken/V8 all become faster.

Comment 1

[David Anderson [:dvander] - inactive, e-mail if emergency]

Sweet! What was the resolution re: JM to Ion calls?

Comment 2

[Jan de Mooij [:jandem]]

(In reply to David Anderson [:dvander] from comment #1)
> Sweet! What was the resolution re: JM to Ion calls?

It uses some simple heuristics (just a few lines of code), e.g. perform a JM -> Ion call only if both caller and callee are Ion-compileable, the callee has at least one loop and the caller is not (very) hot. In the other cases we fallback to JM for the callee. I tried some other things (transitioning to Ion after the script prologue) but these rules are pretty simple (I will explain them in the patch) and gave the best results.

Comment 3

[Jan de Mooij [:jandem]]

Attachment: Patch

Comment 4

[Jan de Mooij [:jandem]]

Attachment: Benchmark results

SS/Kraken/V8 comparison

Comment 5

[Jan de Mooij [:jandem]]

Attachment: Patch

Comment 6

[Jan de Mooij [:jandem]]

Attachment: Benchmark results

Comment 7

[David Anderson [:dvander] - inactive, e-mail if emergency]

Comment on attachment 630525 [details] [diff] [review]
Patch

Review of attachment 630525 [details] [diff] [review]:
-----------------------------------------------------------------

::: js/src/methodjit/Compiler.cpp
@@ +48,5 @@
>      JS_END_MACRO
>  
>  /*
>   * Number of times a script must be called or had a backedge before we try to
> + * inline its calls. This number should match IonMonkey's usesBeforeCompile.

Is it worth hoisting this constant out?

Comment 8

[Jan de Mooij [:jandem]]

http://hg.mozilla.org/projects/ionmonkey/rev/8acbac4d6cfd

(In reply to David Anderson [:dvander] from comment #7)
> 
> Is it worth hoisting this constant out?

I considered it but I couldn't think of a good place to put it: both JITs use the constant even if the other JIT is disabled. Maybe jsscript.h but that also seemed a bit confusing.