Should be no problem. Optinfo hangs off of the JitcodeGlobalTable's
IonEntry entries. There are also IonCacheEntry structs that we could
hang optinfo for ICs from. We are already hanging some opt-info off of
the BaselineEntry structs. These are used when we fail to Ion-compile -
so we attach the failure reason to the BaselineEntry instead, and it
becomes a "reason this code executed in baseline". Hanging optinfo off
of IonCacheEntry structs would look very similar to this.
Kannan
On 2015-02-07 5:35 AM, Jan de Mooij wrote:
Nice! I think this will work well for most performance issues/cliffs I'm
aware of.
Can we add similar instrumentation for ICs? IonBuilder instrumentation will
tell us why we ended up with an IC (that's great), but it'd be neat if we
also tracked why the IC didn't attach a stub, for instance: megamorphism
(too many stubs), "weird" objects on the proto chain (proxies, hooks),
scripted getters/setters etc etc. IC slow paths often show up high in
profiles of websites/frameworks and I think having this information is
essential. Ideally we'd do the same for Baseline ICs :)
Thanks,
Jan
On Fri, Feb 6, 2015 at 1:20 AM, Shu-yu Guo <[email protected]> wrote:
Greetings, fellow subtrahend incrementers!
I recently landed bug 1030389 to track the high-level optimizations
decisions
(i.e., deciding what MIR is emitted) made by IonBuilder. This information
will feed into the profiler and is attached to sampled JIT frames.
Currently, getprop, setprop, getelem, setelem, and calls are tracked. I
should
like to introduce the API here so that upcoming patches of new
optimizations
like the SIMD.js optimizations are tracked from the beginning.
High-level description
----------------------
Optimizations are tracked by bytecode location. The API allows each
bytecode
location to track two things: optimization attempts, and type information.
Each optimization attempt is is a pair of (strategy, outcome). These are
implemented by the enums TrackedStrategy and TrackedOutcome in
js/public/TrackedOptimizationInfo.h. The strategy describes the
optimization
Ion is attempting to emit (e.g., a definite slot load), and the outcome
describes a specific reason for its success or failure (e.g., failed due to
no type info).
Each bytecode location can accumulate a list of attempts. This list is
terminated by the first successful attempt. The slow path is not encoded as
its own attempt pair and is inferred from a list of attempts whose outcomes
are all failures. That is, if only the slow path succeeded, the attempts
list
will all failed attempts.
Each tracked type is a triple of (site, MIR type, type set). The site is
described by the enum TrackedTypeSite.
API
---
Add the specific attempts, outcomes, and type sites you need, if not
already
present, to the enums in js/public/TrackedOptimizationInfo.h.
To start tracking optimizations for a bytecode location,
call |startTrackingOptimizations()|.
Usually, types are tracked in the beginning by
calling |trackTypeInfo(TrackedTypeSite, MIRType, TypeSet *)|.
Before attempting to apply a strategy (e.g., before the call to
getPropTryConstant), call |trackOptimizationAttempt(TrackedStrategy)|. By
default, the outcome of the attempt is "generic failure". To refine the
outcome, call |trackOptimizationOutcome(TrackedOutcome)|.
There is the convenience function |trackOptimizationSuccess()| to track
successes. Be sure to call this on successfully applying an optimization!
In
methods like IonBuilder::jsop_getprop where a series of strategies are
tried
one after another, each |*emitted = true| assignment should be accompanied
by
a call to |trackOptimizationSuccess()|.
All tracking methods are infallible. OOM during tracking disables
optimization
tracking instead.
That's it! Instrumentation bugs also make great first bugs, and I would be
happy to mentor.
--
shu
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