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Performance regression of instanceof in v7 and master #9634
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Could you also create a V8 bug and link to it here ?
I cannot reproduce this regression in Chrome 54.
Now that I test it... neither can I, and in theory they use the same v8 version.
Maybe there is a patch to backport to the v8 version we are using.Found the cause: commit 2a4b068 from last September, cc @addaleax.
Chrome 54 ships the exact same version as node.js master, 5.4.500.41, and I can confirm that it's fast in Chrome and d8 (
./configure --enable-d8) but not in Node.js.I checked with perf(1) and it showed that V8 was spending a phenomenal amount of time in
v8::internal::Object::InstanceOf(), more specifically the code path that checks for the presence of a @@hasInstance method. Here is a minimal test case:function F() {} const hasInstance = Function.prototype[Symbol.hasInstance]; Object.defineProperty(F, Symbol.hasInstance, { value: hasInstance }); for (var o = {}, i = 0; i < 1e8; i++) o instanceof Object;
Basically, if V8 sees that @@hasInstance is used, it starts emitting conservative slow path code.
Reacted by Jiawen GengOh no! :(
We have some possible solutions:
a. revert that fix, but probably it's semver-major. If we could do it semver-minor it will be the best solution.
b. wait until there is a patch from upstream V8, and apply that.It would be nice to a quick post-mortem on this one. How can we spot those before releasing?
Huh… yeah, I did not see that coming.
(sorry, mis-clicked and posted the comment too early)
How can we spot those before releasing?
- Does V8 have benchmarks for this kind of thing? Is running them inside Node helpful?
- Would people from the V8 team have spotted that this is problematic?
- @mcollina I’m curious – how did you spot this?
@mcollina I’m curious – how did you spot this?
I found out that https://github.com/mcollina/bloomrun was 10 times slower in v7 rather than v6. It boiled down to
instanceof, I did not do a git bisect on core, and I should have (that's awesome @bnoordhuis!!!).Truthfully, I didn't bisect. I had a pretty good idea from looking at the perf data where the problem came from and reverting the commit confirmed that. :-)
Reacted by David Mark Clements, Matteo Collina, Richard Lau, Joran Dirk Greef and Gibson FahnestockI think I can come up with a small(ish) mitigation for the problem. Let me have a look.
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on Nov 17, 2016 - changed the title
[-]Performance regression in instanceof in v7 and master[/-][+]Performance regression of instanceof in v7 and master[/+]on Nov 17, 2016 14 remaining items
We need to get this into node v7.
We will probably upgrade to V8 5.5 during the v7 release cycle if we can work out the kinks, see #9618.
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on Nov 22, 2016 - added a commit that references this issue
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on Jan 26, 2017 It looks like this might have regressed back to a 50(ish)x slowdown for
RegExpon the Node 8 nightlies, and for non-builtins (which I added a test for in @mcollina's original example code), it seems to be a 10(ish)x slowdown on both Node 7 and Node 8 nightlies. (Should I open a new issue?)System: Linux 4.9.11 x86_64
$ cat instanceof.js var r = /hello/ console.time('instanceof RegExp') for (var i = 0; i < 100000000; i++) { r instanceof RegExp } console.timeEnd('instanceof RegExp') var o = {} console.time('instanceof Object') for (var i = 0; i < 100000000; i++) { o instanceof Object } console.timeEnd('instanceof Object') function F () {} var f = new F console.time('instanceof F') for (var i = 0; i < 100000000; i++) { f instanceof F } console.timeEnd('instanceof F') $ ~/.nvm/versions/node/v6.10.2/bin/node instanceof.js instanceof RegExp: 127.840ms instanceof Object: 129.514ms instanceof F: 635.539ms $ ~/.nvm/versions/node/v7.9.0/bin/node instanceof.js instanceof RegExp: 163.946ms instanceof Object: 120.818ms instanceof F: 6786.285ms $ ~/.nvm/versions/node/v8.0.0-nightly2017042158066d16d5/bin/node instanceof.js instanceof RegExp: 7501.615ms instanceof Object: 121.429ms instanceof F: 7219.541msThis is https://bugs.chromium.org/p/v8/issues/detail?id=5902
I'll merge this on Monday to 5.8.
Merged to V8 version 5.8: https://chromium.googlesource.com/v8/v8.git/+/e62656ffe685408e06d175ff5f371c8fd2556b58
instanceofchecks has become almost 100 times slower in Node v7+ (and current master)In node v6:
In node v7:
I know this is a problem in V8, but I think it's good to track it here as well.
v8 issue: https://bugs.chromium.org/p/v8/issues/detail?id=5640
cc @fhinkel