JSC should have a low-cost asynchronous disassembler
https://bugs.webkit.org/show_bug.cgi?id=142997
Reviewed by Mark Lam.
Source/JavaScriptCore:
This adds a JSC_asyncDisassembly option that disassembles on a thread. Disassembly
doesn't block execution. Some code will live a little longer because of this, since the
work tasks hold a ref to the code, but other than that there is basically no overhead.
At present, this isn't really a replacement for JSC_showDisassembly, since it doesn't
provide contextual IR information for Baseline and DFG disassemblies, and it doesn't do
the separate IR dumps for FTL. Using JSC_showDisassembly and friends along with
JSC_asyncDisassembly has bizarre behavior - so just choose one.
A simple way of understanding how great this is, is to run a small benchmark like
V8Spider/earley-boyer.
Performance without any disassembly flags: 60ms
Performance with JSC_showDisassembly=true: 477ms
Performance with JSC_asyncDisassembly=true: 65ms
So, the overhead of disassembly goes from 8x to 8%.
Note that JSC_asyncDisassembly=true does make it incorrect to run "time" as a way of
measuring benchmark performance. This is because at VM exit, we wait for all async
disassembly requests to finish. For example, for earley-boyer, we spend an extra ~130ms
after the benchmark completely finishes to finish the disassemblies. This small weirdness
should be OK for the intended use-cases, since all you have to do to get around it is to
measure the execution time of the benchmark payload rather than the end-to-end time of
launching the VM.
- assembler/LinkBuffer.cpp:
(JSC::LinkBuffer::finalizeCodeWithDisassembly):
(JSC::LinkBuffer::wasAlreadyDisassembled):
(JSC::LinkBuffer::didAlreadyDisassemble):
(JSC::DFG::JITCompiler::disassemble):
(JSC::DFG::JITFinalizer::finalize):
(JSC::DFG::JITFinalizer::finalizeFunction):
- disassembler/Disassembler.cpp:
(JSC::disassembleAsynchronously):
(JSC::waitForAsynchronousDisassembly):
- disassembler/Disassembler.h:
- ftl/FTLCompile.cpp:
(JSC::FTL::mmAllocateDataSection):
(JSC::FTL::link):
(JSC::JIT::privateCompile):
- jsc.cpp:
- runtime/Options.h:
- runtime/VM.cpp:
(JSC::VM::~VM):
Source/WTF:
