mirror of
https://github.com/oven-sh/bun
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b6d3768038
### What does this PR do? dropAllLocks causes Thread::yield several times which means more system calls which means more thread switches which means slower ### How did you verify your code works?
68 lines
2.5 KiB
C++
68 lines
2.5 KiB
C++
#include "root.h"
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#include "BunClientData.h"
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#include <JavaScriptCore/VM.h>
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#include <JavaScriptCore/Heap.h>
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extern "C" void Bun__JSC_onBeforeWait(JSC::VM* _Nonnull vm)
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{
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ASSERT(vm);
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const bool previouslyHadAccess = vm->heap.hasHeapAccess();
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// sanity check for debug builds to ensure we're not doing a
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// use-after-free here
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ASSERT(vm->refCount() > 0);
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if (previouslyHadAccess) {
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// Releasing heap access is a balance between:
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// 1. CPU usage
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// 2. Memory usage
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//
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// Not releasing heap access causes benchmarks like
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// https://github.com/oven-sh/bun/pull/14885 to regress due to
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// finalizers not being called quickly enough.
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//
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// Releasing heap access too often causes high idle CPU usage.
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//
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// For the following code:
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// ```
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// setTimeout(() => {}, 10 * 1000)
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// ```
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//
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// command time -v when with defaultRemainingRunsUntilSkipReleaseAccess = 0:
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//
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// Involuntary context switches: 605
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//
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// command time -v when with defaultRemainingRunsUntilSkipReleaseAccess = 5:
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//
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// Involuntary context switches: 350
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//
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// command time -v when with defaultRemainingRunsUntilSkipReleaseAccess = 10:
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//
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// Involuntary context switches: 241
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//
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// Also comapre the #14885 benchmark with different values.
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//
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// The idea here is if you entered JS "recently", running any
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// finalizers that might've been waiting to be run is a good idea.
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// But if you haven't, like if the process is just waiting on I/O
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// then don't bother.
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static constexpr int defaultRemainingRunsUntilSkipReleaseAccess = 10;
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static thread_local int remainingRunsUntilSkipReleaseAccess = 0;
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// Note: usage of `didEnterVM` in JSC::VM conflicts with Options::validateDFGClobberize
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// We don't need to use that option, so it should be fine.
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if (vm->didEnterVM) {
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vm->didEnterVM = false;
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remainingRunsUntilSkipReleaseAccess = defaultRemainingRunsUntilSkipReleaseAccess;
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}
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if (remainingRunsUntilSkipReleaseAccess-- > 0) {
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// Constellation:
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// > If you are not moving a VM to the different thread, then you can aquire the access and do not need to release
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vm->heap.stopIfNecessary();
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vm->didEnterVM = false;
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}
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}
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}
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