Consider turning off the Spectre mitigation for C++ calls
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(Core :: JavaScript Engine: JIT, task)
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(Reporter: jandem, Assigned: jandem)
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(Blocks 2 open bugs)
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(Whiteboard: [sp3])
The LFENCE we emit after a call into C++ is relatively expensive. It was always a pretty big hammer for a more theoretical Spectre issue through C++ code. It might make sense to disable this one by default now that we're shipping Fission on desktop and are getting closer to disabling all of our mitigations in isolated content processes anyway.
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Comment 1•2 years ago
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I think the next step here is to measure the actual performance overhead on the full benchmarks, because I do think this one tends to affect micro-benchmarks more.
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Comment 2•2 years ago
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This is a ~1% improvement on Speedometer 2 and 3.
Comment 3•2 years ago
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1% sounds like a good enough justification to me. Is there anything else that we want to know or think about before doing this?
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Comment 4•2 years ago
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We discussed this a bit more. There's good progress on fixing the remaining blockers for disabling mitigations in Fission content processes, so let's just wait for that. If that work ends up taking longer than expected we can reconsider this.
Updated•2 years ago
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Updated•2 years ago
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Comment 5•2 years ago
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That work has ended up taking longer than I expected. Can we reconsider this?
Comment 6•2 years ago
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As per Jeff's proposal let's re-open. It feels to me like we shouldn't let this linger longer than needed.
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Comment 7•2 years ago
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(In reply to Jeff Muizelaar [:jrmuizel] from comment #5)
That work has ended up taking longer than I expected. Can we reconsider this?
We talked about this a bit. The ORB work is progressing well, changes have landed, and they're now waiting for telemetry results. Let's hold off for a few more weeks until we have more information on that effort. It sounds like we should have more information on that soon, but I'll leave the needinfo to check on this.
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Updated•1 year ago
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