Don't copy VMBuiltinFunctionsArray into each VMContext#3741
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alexcrichton merged 2 commits intobytecodealliance:mainfrom Jan 28, 2022
Merged
Don't copy VMBuiltinFunctionsArray into each VMContext#3741alexcrichton merged 2 commits intobytecodealliance:mainfrom
VMBuiltinFunctionsArray into each VMContext#3741alexcrichton merged 2 commits intobytecodealliance:mainfrom
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This is another PR along the lines of "let's squeeze all possible performance we can out of instantiation". Before this PR we would copy, by value, the contents of `VMBuiltinFunctionsArray` into each `VMContext` allocated. This array of function pointers is modestly-sized but growing over time as we add various intrinsics. Additionally it's the exact same for all `VMContext` allocations. This PR attempts to speed up instantiation slightly by instead storing an indirection to the function array. This means that calling a builtin intrinsic is a tad bit slower since it requires two loads instead of one (one to get the base pointer, another to get the actual address). Otherwise though `VMContext` initialization is now simply setting one pointer instead of doing a `memcpy` from one location to another. With some macro-magic this commit also replaces the previous implementation with one that's more `const`-friendly which also gets us compile-time type-checks of libcalls as well as compile-time verification that all libcalls are defined. Overall, as with bytecodealliance#3739, the win is very modest here. Locally I measured a speedup from 1.9us to 1.7us taken to instantiate an empty module with one function. While small at these scales it's still a 10% improvement!
fitzgen
approved these changes
Jan 28, 2022
cfallin
approved these changes
Jan 28, 2022
crates/runtime/src/vmcontext.rs
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| for i in 0..ptrs.len() { | ||
| debug_assert!(ptrs[i] != 0, "index {} is not initialized", i); | ||
| impl VMBuiltinFunctionsArray { | ||
| pub fn new() -> &'static Self { |
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Rather than new(), can we call this static_instance() or something like that? As written it was somewhat concerning to read VMBuiltinFunctionsArray::new() in the initialization path -- it looked like an allocation of an owned thing.
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Aha looks like I can do one better and have const INIT: VMBuiltinFunctionsArray = ...!
bjorn3
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Jan 28, 2022
| delta: u64, | ||
| memory_index: u32, | ||
| ) -> usize { | ||
| ) -> *mut u8 { |
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This function doesn't return an actual pointer, right?
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Correct, this is just how the type-checking with the macro worked out.
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…lliance#3741) * Don't copy `VMBuiltinFunctionsArray` into each `VMContext` This is another PR along the lines of "let's squeeze all possible performance we can out of instantiation". Before this PR we would copy, by value, the contents of `VMBuiltinFunctionsArray` into each `VMContext` allocated. This array of function pointers is modestly-sized but growing over time as we add various intrinsics. Additionally it's the exact same for all `VMContext` allocations. This PR attempts to speed up instantiation slightly by instead storing an indirection to the function array. This means that calling a builtin intrinsic is a tad bit slower since it requires two loads instead of one (one to get the base pointer, another to get the actual address). Otherwise though `VMContext` initialization is now simply setting one pointer instead of doing a `memcpy` from one location to another. With some macro-magic this commit also replaces the previous implementation with one that's more `const`-friendly which also gets us compile-time type-checks of libcalls as well as compile-time verification that all libcalls are defined. Overall, as with bytecodealliance#3739, the win is very modest here. Locally I measured a speedup from 1.9us to 1.7us taken to instantiate an empty module with one function. While small at these scales it's still a 10% improvement! * Review comments
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This is another PR along the lines of "let's squeeze all possible
performance we can out of instantiation". Before this PR we would copy,
by value, the contents of
VMBuiltinFunctionsArrayinto eachVMContextallocated. This array of function pointers is modestly-sizedbut growing over time as we add various intrinsics. Additionally it's
the exact same for all
VMContextallocations.This PR attempts to speed up instantiation slightly by instead storing
an indirection to the function array. This means that calling a builtin
intrinsic is a tad bit slower since it requires two loads instead of one
(one to get the base pointer, another to get the actual address).
Otherwise though
VMContextinitialization is now simply setting onepointer instead of doing a
memcpyfrom one location to another.With some macro-magic this commit also replaces the previous
implementation with one that's more
const-friendly which also gets uscompile-time type-checks of libcalls as well as compile-time
verification that all libcalls are defined.
Overall, as with #3739, the win is very modest here. Locally I measured
a speedup from 1.9us to 1.7us taken to instantiate an empty module with
one function. While small at these scales it's still a 10% improvement!