Hi all.
I am trying to figure out what the effect of the agent-function is on
the efficiency of concurrency. Here is something I do not really
understand. I've a fibonacci function and a simple multiplication,
both are wrapped in their respective dotimes 100k loop.
However, on this 4core machine, the fib behaves as I would expect when
I scale up the number of threads, while the multiplication barely
seems to benefit from the 4 cores. The only difference I see between
the two functions is that the fib is recursive, but I am not quite
sure why that would matter.
Can anyone shine a light?
(defn fib [n]
"nonoptimized fib"
(if (<= n 1)
1
(+ (fib (- n 1)) (fib (- n 2)))))
(defn loopfib [n]
(dotimes [i 100000]
(fib n)))
(defn loopmult [n]
(dotimes [i 100000]
(* n n n n n 5000 5000 4000 3000 9000)))
(dotimes [t 12]
(println "threads: " t)
(time
(let [agents (for [i (range t)] (agent 4))]
(do
(doseq [a agents] (send-off a loopfib))
(apply await agents))))
(time
(let [agents (for [i (range t)] (agent 4))]
(do
(doseq [a agents] (send-off a loopmult))
(apply await agents)))))
result:
threads: 0
"Elapsed time: 0.279713 msecs"
"Elapsed time: 0.38143 msecs"
threads: 1
"Elapsed time: 205.458949 msecs"
"Elapsed time: 209.625273 msecs"
threads: 2
"Elapsed time: 205.610849 msecs"
"Elapsed time: 357.785344 msecs"
threads: 3
"Elapsed time: 205.05658 msecs"
"Elapsed time: 401.39515 msecs"
threads: 4
"Elapsed time: 221.140317 msecs"
"Elapsed time: 469.746969 msecs"
threads: 5
"Elapsed time: 309.472848 msecs"
"Elapsed time: 597.872393 msecs"
threads: 6
"Elapsed time: 336.087848 msecs"
"Elapsed time: 714.874749 msecs"
threads: 7
"Elapsed time: 382.883045 msecs"
"Elapsed time: 846.888746 msecs"
threads: 8
"Elapsed time: 442.588196 msecs"
"Elapsed time: 960.687669 msecs"
threads: 9
"Elapsed time: 478.862175 msecs"
"Elapsed time: 1094.892017 msecs"
threads: 10
"Elapsed time: 514.380769 msecs"
"Elapsed time: 1219.219582 msecs"
threads: 11
"Elapsed time: 580.265387 msecs"
"Elapsed time: 1361.204858 msecs"
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