hmm.jl

using BenchmarkTools
A = rand(10000)
B = Vector[rand(10) for i = 1:1000]
C = rand(10,1000)

D = rand(10000)
E = Vector[rand(10) for i = 1:1000]
F = rand(10, 1000)

function fast!(a, c)
    for j = 1:1000
        a[1+(j-1)*10:j*10] = c[1+(j-1)*10:j*10]'*rand(10,10)
    end
end

function fast_slow!(c, f)
    for j = 1:1000
        c[:, j] = f[:, j]'*rand(10,10)
    end
end

function slow!(b, d)
    for j = 1:1000
        for i = 1:10
            b[j][:] = d[j]'*rand(10,10)
        end
    end
end

fast!(A, D)
fast_slow!(C, F)
slow!(B, E)
@benchmark fast!(A, C)
@benchmark fast_slow!(C, F)
@benchmark slow!(B, E)