Slowdown of a function executed remotely (Julia issue #6686)

slowremote.jl

module SlowRemoteExecution

type W
    J::Vector{BitVector}
    W(N::Int, K::Int) = new([randbool(N) for k=1:K])
end

function inner(ws::Vector{W}, X::Vector{BitVector})
    r = 0
    @time begin
        for x in X, w in ws
            J = w.J
            s = 0
            for j in J
                s += dot(j, x) > 120
            end
            r += s > 50
        end
    end
    return r
end

function inner_evenslower(ws::Vector{W}, X::Vector{BitVector})
    r = 0
    @time begin
        Js = [w.J for w in ws]
        for x in X, J in Js
            s = 0
            for j in J
                s += dot(j, x) > 120
            end
            r += s > 50
        end
    end
    return r
end

function inner_fastonremote(ws::Vector{W}, X::Vector{BitVector})
    r = 0
    @time begin
        Jscs = [[j.chunks for j in w.J] for w in ws]
        for x in X
            xc = x.chunks
            for Jcs in Jscs
                s = 0
                for jc in Jcs
                    d = 0
                    l = length(jc)
                    for i = 1:l
                        d += count_ones(jc[i] & xc[i])
                    end
                    s += d > 120
                end
                r += s > 50
            end
        end
    end
    return r
end

function outer(ws::Vector{W}, X::Vector{BitVector})

    println("inner on local process")
    println("----------------------")
    @time x1 = remotecall_fetch(1, inner, ws, X)
    println()

    println("inner on worker")
    println("---------------")
    @time x2 = remotecall_fetch(2, inner, ws, X)
    println()

    println("inner_evenslower on local process")
    println("---------------------------------")
    @time x1s = remotecall_fetch(1, inner_evenslower, ws, X)
    println()

    println("inner_evenslower on worker")
    println("--------------------------")
    @time x2s = remotecall_fetch(2, inner_evenslower, ws, X)
    println()

    println("inner_fastonremote on local process")
    println("-----------------------------------")
    @time x1f = remotecall_fetch(1, inner_fastonremote, ws, X)
    println()

    println("inner_fastonremote on worker")
    println("----------------------------")
    @time x2f = remotecall_fetch(2, inner_fastonremote, ws, X)
    println()

    @assert x1 == x2 == x1s == x2s == x1f == x2f

end

function tst()
    srand(1)
    N = 500
    K1 = 100
    K2 = 200
    M = 1_000
    ws = [W(N, K1) for i = 1:K2]
    X = [randbool(N) for i = 1:M]

    outer(ws, X)
end

end

slowremote_run.txt

julia> SlowRemoteExecution.tst()
inner on local process
----------------------
elapsed time: 0.589470459 seconds (0 bytes allocated)
elapsed time: 0.589635775 seconds (424 bytes allocated)

inner on worker
---------------
	From worker 2:	elapsed time: 1.615534087 seconds (0 bytes allocated)
elapsed time: 2.12067934 seconds (38298756 bytes allocated)

inner_evenslower on local process
---------------------------------
elapsed time: 0.587374153 seconds (2048 bytes allocated)
elapsed time: 0.587548044 seconds (2488 bytes allocated)

inner_evenslower on worker
--------------------------
	From worker 2:	elapsed time: 2.265180296 seconds (2048 bytes allocated)
elapsed time: 2.810449319 seconds (38297416 bytes allocated)

inner_fastonremote on local process
-----------------------------------
elapsed time: 0.582856348 seconds (6581248 bytes allocated)
elapsed time: 0.583044048 seconds (6581688 bytes allocated)

inner_fastonremote on worker
----------------------------
	From worker 2:	elapsed time: 0.569549788 seconds (6581248 bytes allocated)
elapsed time: 1.108767959 seconds (38297624 bytes allocated)