Add `setcpuaffinity(cmd, cpus)` for setting CPU affinity of subprocesses #42469

tkf · 2021-10-02T03:53:40Z

While working on implementing tests for #42340, I thought it'd make sense to add a Julia API to spawn processes with an explicit CPU affinity since libuv already can do this. It may also be useful for process-based parallelism libraries like Distributed and Dagger.

So, this patch adds a new API:

setcpuaffinity(original_command::Cmd, cpus) -> command::Cmd
Set the CPU affinity of the command by a list of CPU IDs (1-based) cpus. Passing cpus = nothing means to unset the CPU affinity if the original_command has any.

This is supported on Unix and Windows but not in macOS.

Example:

julia> run(setcpuaffinity(`sh -c 'taskset -p $$'`, [1, 2, 5]));
pid 2273's current affinity mask: 13

julia> 0b010011
0x13

We can now remove taskset from the test dependency.

Side notes: The behavior of cpus = nothing with JULIA_EXCLUSIVE=1 is currently badly defined/implemented #42338. So, we'd need to be careful when documenting its behavior.

What do you think? Is it an appropriate API for Julia Base?

base/cmd.jl

test/print_process_affinity.jl

test/threads.jl

Co-authored-by: Jameson Nash <vtjnash@gmail.com>

KristofferC · 2021-10-02T21:34:40Z

base/cmd.jl

+julia> run(setcpuaffinity(`sh -c 'taskset -p \$\$'`, [1, 2, 5]));
+pid 2273's current affinity mask: 13
+
+julia> 0b010011


The logic required to go from the first command to understand the point of the second feels a bit large here.

Thanks, good point. I added a bit more explanations in the latest commit.

tkf · 2021-10-02T22:21:38Z

test/show.jl

+@testset "Cmd" begin
+    @test sprint(show, `true`) == "`true`"
+    @test sprint(show, setenv(`true`, "A" => "B")) == """setenv(`true`,["A=B"])"""
+    @test sprint(show, setcpuaffinity(`true`, [1, 2])) == "setcpuaffinity(`true`,[1, 2])"
+    @test sprint(show, setenv(setcpuaffinity(`true`, [1, 2]), "A" => "B")) ==
+          """setenv(setcpuaffinity(`true`,[1, 2]),["A=B"])"""
+end


I couldn't find where show(::IO, ::Cmd) was tested. It looks like the original commit dee7f6c didn't add the test for show with setenv. So, I just threw this in for completeness.

tkf · 2021-10-14T00:25:10Z

@vtjnash Can you revisit the above coment? Is it good to go?

vtjnash

Some suggestions

base/cmd.jl

vtjnash · 2021-10-14T14:31:57Z

base/cmd.jl

+setcpuaffinity(cmd::Cmd, ::Nothing) = Cmd(cmd; cpus = nothing)
+setcpuaffinity(cmd::Cmd, cpus) = Cmd(cmd; cpus = collect(Int, cpus))


Suggested change

setcpuaffinity(cmd::Cmd, ::Nothing) = Cmd(cmd; cpus = nothing)

setcpuaffinity(cmd::Cmd, cpus) = Cmd(cmd; cpus = collect(Int, cpus))

setcpuaffinity(cmd::Cmd, ::Nothing) = Cmd(cmd; cpus = nothing)

setcpuaffinity(cmd::Cmd, cpus::AbstractVector{Bool}) = Cmd(cmd; cpus = findall(cpus))

setcpuaffinity(cmd::Cmd, cpus::AbstractVector) = Cmd(cmd; cpus = convert(Vector{UInt16}, cpus))

setcpuaffinity(cmd::Cmd, cpus) = setcpuaffinity(cmd, collect(cpus)::AbstractVector)

I'm against dispatching on Bool element type to change the meaning (in general). It will change the behavior between cpus = Bool[true] and cpus = Integer[true] (or Any[true]). I prefer to add a distinct function like setcpuaffinitymask or maybe a Mask type for supporting this.

test/print_process_affinity.jl

test/show.jl

test/print_process_affinity.jl

Co-authored-by: Jameson Nash <vtjnash@gmail.com>

test/threads.jl

tkf · 2021-10-15T23:31:41Z

@vtjnash Can you check my comments above?

vtjnash

Do we know what happened on FreeBSD? The CI logs make it seem like it hung in the precompile tests, before getting to testing the new code.

test/print_process_affinity.jl

test/threads.jl

Co-authored-by: Jameson Nash <vtjnash@gmail.com>

tkf · 2021-11-10T06:37:38Z

I have no idea what's happening in FreeBSD but I think the CI was older than the recent fixes for FreeBSD. I merged the master branch to see if it shows something new.

tkf · 2021-11-10T23:35:48Z

In win64 we are getting

ERROR: LoadError: IOError: getaffinity: bad file descriptor (EBADF)
Stacktrace:
 [1] uv_error
   @ .\libuv.jl:97 [inlined]
 [2] uv_thread_getaffinity()
   @ Main C:\buildbot\worker-tabularasa\tester_win64\build\share\julia\test\print_process_affinity.jl:18
 [3] print_process_affinity()
   @ Main C:\buildbot\worker-tabularasa\tester_win64\build\share\julia\test\print_process_affinity.jl:25
 [4] top-level scope
   @ C:\buildbot\worker-tabularasa\tester_win64\build\share\julia\test\print_process_affinity.jl:30
in expression starting at C:\buildbot\worker-tabularasa\tester_win64\build\share\julia\test\print_process_affinity.jl:29

(which is the same as #42469 (comment) but with a better error message).

I guess this requires libuv/libuv#3357 too.

tkf · 2021-12-16T02:32:26Z

Now that #43219 pulls in the fix libuv/libuv#3357, the test works in Windows CI.

@vtjnash Good to go?

base/cmd.jl

test/threads.jl

…ses (JuliaLang#42469) Support running commands with cpumask.

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Support running commands with cpumask

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Apply suggestions from code review

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Co-authored-by: Jameson Nash <vtjnash@gmail.com>

Rename: setcpus -> setcpuaffinity

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Include it in docs and news

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tkf changed the title ~~RFC: add setcpus(cmd, cpus) for setting CPU affinity of subprocesses~~ RFC: add setcpuaffinity(cmd, cpus) for setting CPU affinity of subprocesses Oct 2, 2021

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Include examples in the docstring

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Delay converting to cpumask; define show

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Fill between the lines in the docstring

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Use uv_thread_getaffinity when --threads=auto #42340

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Merge branch 'master' into cpumask

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tkf changed the title ~~RFC: add setcpuaffinity(cmd, cpus) for setting CPU affinity of subprocesses~~ Add setcpuaffinity(cmd, cpus) for setting CPU affinity of subprocesses Oct 14, 2021

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Fix cpus type

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tkf added 4 commits October 14, 2021 19:17

Add compat annotation

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Fix show

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Fix a typo

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Don't run test with uv_thread_getaffinity on Windows

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Mention that it's Linux-only for now

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Merge branch 'master' into cpumask

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Through a proper error in print_process_affinity.jl

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Co-authored-by: Jameson Nash <vtjnash@gmail.com>

Fix print_process_affinity.jl for Windows

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Merge branch 'master' into cpumask

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Merge branch 'master' into cpumask

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Add setcpuaffinity(cmd, cpus) for setting CPU affinity of subproces…

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…ses (JuliaLang#42469) Support running commands with cpumask.

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Add setcpuaffinity(cmd, cpus) for setting CPU affinity of subproces…

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…ses (JuliaLang#42469) Support running commands with cpumask.

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Add `setcpuaffinity(cmd, cpus)` for setting CPU affinity of subprocesses #42469

Add `setcpuaffinity(cmd, cpus)` for setting CPU affinity of subprocesses #42469

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tkf commented Dec 16, 2021

		setcpuaffinity(cmd::Cmd, ::Nothing) = Cmd(cmd; cpus = nothing)
		setcpuaffinity(cmd::Cmd, cpus) = Cmd(cmd; cpus = collect(Int, cpus))

Add setcpuaffinity(cmd, cpus) for setting CPU affinity of subprocesses #42469

Add setcpuaffinity(cmd, cpus) for setting CPU affinity of subprocesses #42469

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Add `setcpuaffinity(cmd, cpus)` for setting CPU affinity of subprocesses #42469

Add `setcpuaffinity(cmd, cpus)` for setting CPU affinity of subprocesses #42469

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