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Sign upbabylon drumming demo thrashes the ion JIT #25971
Comments
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The following script shows a hotspot of compiling and a really long tail of scripts that get compiled once: import sys
scripts = {}
with open(sys.argv[1]) as f:
for line in f.readlines():
if not line.startswith('[IonScripts]'):
continue
print(line)
if 'Compiling' in line:
script = line.split()[3]
if not script in scripts:
scripts[script] = 0
scripts[script] += 1
ordered = sorted(scripts.items(), key=lambda item: item[1])
for (script, count) in ordered:
print(script.split('/')[-1] + ": " + str(count)) |
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One set of frequent bailouts turns out to be calling |
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The following script identifies the most common invalidations from a log with import sys
scripts = {}
with open(sys.argv[1]) as f:
for line in f.readlines():
if not line.startswith('[IonInvalidate]'):
continue
print(line)
if 'Invalidate ' in line:
script = line.split()[2]
if not script in scripts:
scripts[script] = 0
scripts[script] += 1
ordered = sorted(scripts.items(), key=lambda item: item[1])
for (script, count) in ordered:
print(script.split('/')[-1] + ": " + str(count)) |
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I've written up my steps for diagnosing so far as https://github.com/servo/servo/wiki/Diagnosing-SpiderMonkey-JIT-issues. |
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We've tracked this down to a reproducible bailout in the spidermonkey arm64 simulator running this snippet: var intensity = 1;
var Color3 = function(r) {
this.r = r;
};
Color3.prototype.scale = function(t) {
this.r = this.r * t;
};
var groundColor = new Color3(0);
for (var i = 0; i < 10000; i++) {
groundColor.scale(intensity);
}This means there's a codegen bug in ionmonkey in the arm64 backend for integer multiplication, and a JS team member is looking into it. |
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Turns out this TODO has significant implications: "the answer to your puzzle appears to be "ionmonkey is incredibly dumb on arm64 when compiling integer multiplications that produce zero"" |
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The patch from https://phabricator.services.mozilla.com/D67485 lets us hit ~40 FPS once the JIT settles down after a few seconds. |
Here's the jitspew output when I run the demo (even when it's showing the default view in windowed mode with no change in rendering):