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Remove dynamic dispatch from _wait/wait2 #50202

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Jul 5, 2023
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While looking at the performance off:

using Base.Iterators: partition

function axpy_per_core!(y, a, x)
    indices = eachindex(y,x)
    tasks_per_thread = 1 # customize this as needed. More tasks have more overhead, but better load balancing
    chunk_size = max(1, length(indices) ÷ (tasks_per_thread * Threads.nthreads()))
    indices_chunks = partition(indices, chunk_size)

    @sync for chunk in indices_chunks
        Threads.@spawn begin
            for i in chunk
                y[i] = muladd(a, x[i], y[i])
            end
        end
    end
end

y = rand(10_000);
x = rand(10_000);

axpy_per_core!(y, 2.0, x)

Gabrield and I noticed that a not-insignificant amount of time is spent on the dynamic dispatch.
As far as we can tell we are gurantueed that donenotify is a ThreadSynchronizer.
See task_done_hook.

Co-authored-by: Gabriel Baraldi <baraldigabriel@gmail.com>
@vchuravy vchuravy added performance Must go faster multithreading Base.Threads and related functionality labels Jun 16, 2023
@vchuravy vchuravy requested a review from vtjnash June 16, 2023 22:51
@KristofferC KristofferC added the backport 1.10 Change should be backported to the 1.10 release label Jul 5, 2023
@KristofferC KristofferC merged commit e025877 into master Jul 5, 2023
@KristofferC KristofferC deleted the vc/stable_wait branch July 5, 2023 10:11
KristofferC pushed a commit that referenced this pull request Jul 11, 2023
Co-authored-by: Gabriel Baraldi <baraldigabriel@gmail.com>
(cherry picked from commit e025877)
KristofferC added a commit that referenced this pull request Jul 24, 2023
Backported PRs:
- [x] #50411 <!-- Fix weird dispatch of * with zero arguments -->
- [x] #50202 <!-- Remove dynamic dispatch from _wait/wait2 -->
- [x] #50064 <!-- Fix numbered prompt with input only with comment -->
- [x] #50026 <!-- Store heapsnapshot files in tempdir() instead of
current directory -->
- [x] #50402 <!-- Add CPU feature helper function -->
- [x] #50387 <!-- update newpages pointer after actually sweeping pages
-->
- [x] #50424 <!-- avoid potential type-instability in _replace_(str,
...) -->
- [x] #50444 <!-- Optimize getfield lowering to avoid boxing in some
cases -->
- [x] #50474 <!-- docs: Fix a `!!! note` which was miscapitalized -->
- [x] #50466 <!-- relax assertion involving pg->nold to reflect that it
may be a bit in… -->
- [x] #50490 <!-- Fix compat annotation for italic printstyled -->
- [x] #50488 <!-- fix typo in `Base.isassigned` with `Tridiagonal` -->
- [x] #50476 <!-- Profile: Add specifying dir for `take_heap_snapshot`
and handling if current dir is unwritable -->
- [x] #50461 <!-- fix typo in the --gcthreads argument description -->
- [x] #50528 <!-- ssair: Correctly handle stmt insertion at end of basic
block -->
- [x] #50533 <!-- ensure internal_obj_base_ptr checks whether objects
past freelist pointer are in freelist -->
- [x] #49322 <!-- improve cat design / performance -->
- [x] #50540 <!-- gc: remove over-eager assertion -->
- [x] #50542 <!-- gf: remove unnecessary assert cycle==depth -->
- [x] #50559 <!-- Expand kwcall lowering positional default check to
vararg -->
- [x] #50058 <!-- Add unwrapping mechanism for triangular mul and solves
-->
- [x] #50551 <!-- typeintersect: also record chained `innervars` -->
- [x] #50552 <!-- read(io, Char): fix read with too many leading ones
-->
- [x] #50541 <!-- precompile: ensure globals are not accidentally
created where disallowed -->
- [x] #50576 <!-- use atomic compare exchange when setting the GC
mark-bit -->
- [x] #50578 <!-- gf: make method overwrite/delete an error during
precompile -->
- [x] #50516 <!-- Fix visibility of assert on GCC12/13 -->
- [x] #50597 <!-- Fix memory corruption if task is launched inside
finalizer -->
- [x] #50591 <!-- build: fix various makefile bugs -->
- [x] #50599 <!-- faster invalid object lookup in conservative gc -->
- [x] #50634 <!-- 🤖 [master] Bump the SparseArrays stdlib from b4b0e72
to 99c99b4 -->
- [x] #50639 <!-- Backport LLVM patches to fix various issues. -->
- [x] #50546 <!-- Revert storage of method instance in LineInfoNode -->
- [x] #50631 <!-- Shift DCE pass to optimize imaging mode code better
-->
- [x] #50525 <!-- only check that values are finite in `generic_lufact`
when `check=true` -->
- [x] #50587 <!-- isassigned for ranges with BigInt indices -->
- [x] #50144 <!-- Page based heap size heuristics -->


Need manual backport:
- [ ] #50595 <!-- Rename ENV variable `JULIA_USE_NEW_PARSER` ->
`JULIA_USE_FLISP_PARSER` -->



Non-merged PRs with backport label:
- [ ] #50637 <!-- Remove SparseArrays legacy code -->
- [ ] #50618 <!-- inference: continue const-prop' when concrete-eval
returns non-inlineable -->
- [ ] #50598 <!-- only limit types in stack traces in the REPL -->
- [ ] #50594 <!-- Disallow non-index Integer types in isassigned -->
- [ ] #50568 <!-- `Array(::AbstractRange)` should return an `Array` -->
- [ ] #50523 <!-- Avoid generic call in most cases for getproperty -->
- [ ] #50172 <!-- print feature flags used for matching pkgimage -->
@KristofferC KristofferC removed the backport 1.10 Change should be backported to the 1.10 release label Jul 24, 2023
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