Pelemay Fast Parallel map has just been released!

zacky1972 · December 27, 2020, 9:48am

This is a present of the end of year for Elixir programmers from me: The new package “Pelemay Fast Parallel map” has been released! It drives multi cores and is 3x faster than Enum! Check it out, soon!

Pelemay Fast Parallel map (or pelemay_fp) - Fast parallel map function for Elixir

Pelemay Fast Parallel map: provides fast Parallel map function, similar to the Enum module, although computations will be executed in parallel using Process.spawn/4.

Here is a quick example on how to calculate the square of each element with PelemayFp:

list
|> PelemayFp.map(& &1 * &1)

We conducted performance evaluation of PelemayFp, Pelemay, Flow, Enum and Pmap on iMac Pro (2017):

## PelemayFpBench
benchmark name          iterations   average time 
PelemayFp                      200   10177.85 µs/op
Pelemay                        100   16762.24 µs/op
PelemayFp and Pelemay          100   18532.70 µs/op
Flow (without sorting)         100   18731.43 µs/op
Enum                            50   31283.36 µs/op
Flow (with sorting)             10   105091.00 µs/op
Pmap                             1   1213749.00 µs/op

Thanks! A happy new year!

Eiji · December 27, 2020, 10:12am

Nice idea! Here goes something from me …

zacky1972 · December 27, 2020, 10:14am

Thank you!
It’s quite a strange behavior…

LostKobrakai · December 27, 2020, 11:05am

How does this compare to Task.async_stream, which would be the core way of separating computations into different processes?

zacky1972 · December 27, 2020, 11:28am

Thank you. TIL Task.async_stream.

zacky1972 · December 27, 2020, 11:29am

I may have misunderstood the specification of spawn_monitor . Perhaps once a child process is launched by spawn_monitor , will it be started again even if it quit by executing exit(:normal) ?

Eiji · December 27, 2020, 12:47pm

@LostKobrakai I tried Task.async_stream/2 in few benchmarks, but results are not as good as expected …

Edit Updated benchmarks:

pelemay_fp: benchee

benchmark.exs

defmodule Benchmark do
  @list Enum.to_list(1..100)

  def run do
    Benchee.run(
      %{
        "enum" => fn -> Enum.map(@list, &logistic_map_10/1) end,
        "pelemay_fp" => fn -> PelemayFp.map(@list, &logistic_map_10/1) end,
        "stream" => fn -> @list |> Stream.map(&logistic_map_10/1) |> Stream.run() end,
        "task_async_stream" => fn -> @list |> Task.async_stream(&logistic_map_10/1) |> Enum.to_list() end
      },
      time: 10,
      memory_time: 2
    )    
  end

  defp logistic_map_10(v) do
    logistic_map(v)
    |> logistic_map()
    |> logistic_map()
    |> logistic_map()
    |> logistic_map()
    |> logistic_map()
    |> logistic_map()
    |> logistic_map()
    |> logistic_map()
    |> logistic_map()
  end

  defp logistic_map(v) do
    rem(22 * v * (v + 1), 6_700_417)
  end
end

Benchmark.run()

mix run benchmark.exs

Operating System: Linux
CPU Information: Intel(R) Core(TM) i7-3630QM CPU @ 2.40GHz
Number of Available Cores: 8
Available memory: 15.53 GB
Elixir 1.11.2
Erlang 23.2.1

Benchmark suite executing with the following configuration:
warmup: 2 s
time: 10 s
memory time: 2 s
parallel: 1
inputs: none specified
Estimated total run time: 56 s

Benchmarking enum...
Benchmarking pelemay_fp...
Benchmarking stream...
Benchmarking task_async_stream...

Name                        ips        average  deviation         median         99th %
pelemay_fp              37.47 K       26.69 μs  ±5358.81%        9.10 μs      295.71 μs
enum                    28.89 K       34.61 μs    ±41.28%       31.53 μs       57.92 μs
stream                  24.44 K       40.91 μs   ±251.74%       35.87 μs       65.61 μs
task_async_stream        0.43 K     2342.98 μs    ±33.40%     2127.96 μs     4539.60 μs

Comparison: 
pelemay_fp              37.47 K
enum                    28.89 K - 1.30x slower +7.92 μs
stream                  24.44 K - 1.53x slower +14.22 μs
task_async_stream        0.43 K - 87.78x slower +2316.29 μs

Memory usage statistics:

Name                      average  deviation         median         99th %
pelemay_fp                2.10 KB     ±0.00%        2.10 KB        2.10 KB
enum                      1.56 KB     ±0.00%        1.56 KB        1.56 KB
stream                    4.35 KB     ±0.00%        4.35 KB        4.35 KB
task_async_stream       120.59 KB     ±0.69%      120.73 KB      121.70 KB

Comparison: 
pelemay_fp                2.10 KB
enum                      1.56 KB - 0.74x memory usage -0.53906 KB
stream                    4.35 KB - 2.07x memory usage +2.25 KB
task_async_stream       120.59 KB - 57.38x memory usage +118.49 KB

pelemay_fp_benchmark: pelemay_fp_benchmark

mix bench

Settings:
  duration:      1.0 s

## PelemayFpBench
[13:29:41] 1/7: Async stream
[13:29:43] 2/7: Enum
[13:29:45] 3/7: Flow (with sorting)
[13:29:46] 4/7: Flow (without sorting)
[13:29:49] 5/7: PelemayFp
[13:29:50] 6/7: Pmap
[13:29:53] 7/7: Stream

Finished in 14.4 seconds

## PelemayFpBench
benchmark name          iterations   average time 
PelemayFp                      100   12119.25 µs/op
Flow (without sorting)         100   23138.32 µs/op
Enum                            50   29528.56 µs/op
Stream                          50   40619.40 µs/op
Flow (with sorting)             10   109108.60 µs/op
Pmap                             2   878048.00 µs/op
Async stream                     1   2257371.00 µs/op

al2o3cr · December 27, 2020, 4:47pm

PelemayFp splits the incoming value into chunks of 12000, so I’m not sure what this benchmark demonstrates - it will only spawn one worker. FWIW, the code in https://github.com/zeam-vm/pelemay_fp_benchmark/blob/main/bench/pelemay_fp_bench.exs use a limit of 100k.

zacky1972 · December 27, 2020, 5:55pm

Fix this issue. Thanks!

zacky1972 · December 27, 2020, 6:12pm

I added benchmark of Stream and Task.async_stream. Thanks

## PelemayFpBench
benchmark name          iterations   average time 
PelemayFp                      100   14143.22 µs/op
Pelemay                        100   18627.19 µs/op
PelemayFp and Pelemay          100   20414.04 µs/op
Flow (without sorting)         100   20720.33 µs/op
Enum                            50   31957.12 µs/op
Stream                          50   38792.98 µs/op
Flow (with sorting)             10   116906.90 µs/op
Pmap                             2   830539.50 µs/op
Task.async_stream                1   1099493.00 µs/op

al2o3cr · December 28, 2020, 1:09am

I tried out some changes to increase the per-element workload, because there’s a fair bit of overhead with starting communicating processes. See notes in https://github.com/zeam-vm/pelemay_fp_benchmark/pull/1

zacky1972 · December 28, 2020, 8:16am

Thank you for your contribution.

As you mentioned, the threshold parameter is very sensitive to performance, so I guess it requires some kind of parameter optimization technology for practical usage. I have a plan to develop such a technology.

zacky1972 · December 28, 2020, 8:47am

PelemayFp that fixed the issue that unreceived messages remained has just been released!

dom · January 1, 2021, 2:02am

Why is there such a big performance difference with the pmap here:

github.com

zeam-vm/pelemay_fp_benchmark/blob/main/lib/pelemay_fp_benchmark/parallel.ex

defmodule Parallel do
  def pmap(collection, func) do
    collection
    |> Enum.map(&Task.async(fn -> func.(&1) end))
    |> Enum.map(&Task.await/1)
  end
end

Is it because the particular benchmark you’re doing benefits from batching? If so, could you get the same benefit by calling Enum.chunk_every before the map, and Enum.concat after? (modifying the async task to call Enum.map as well)

zacky1972 · January 1, 2021, 6:04am

This code is from Programming Elixir by Dave Thomas.
It is simple, but has such a performance bottleneck, which you mentioned.

I tried to use Enum.chunk_every before implementing PelemayFp, but it was slower than I expected. After the new year’s holidays, I’ll show it to you.

dom · January 1, 2021, 9:46am

Oh you’re right, I played with it a bit and Enum.chunk_every is quite slow because the implementation is generic for all enumerables. If I write a specialized version just for lists instead, then I get similar timings for PelemayFp, Task.async_stream, and pmap (with batches of 12,000 items).

I noticed a small detail, the benchmark code is using a module constant for the list:

@list Enum.to_list(1..100000)

This may affect the timing a bit since constants aren’t subject to garbage collection and don’t get copied when they’re sent from one process to another, unlike variable data.

zacky1972 · January 3, 2021, 8:09pm

@list Enum.to_list(1..100000)
This may affect the timing a bit since constants aren’t subject to garbage collection and don’t get copied when they’re sent from one process to another, unlike variable data.

To solve it, I guess it should be implemented using before_each_bench and after_each_bench.

zacky1972 · January 5, 2021, 7:36pm

I’ve implemented PelemayFp.ParallelSplitter.split/7 as a faster integrated function like Enum.chunck_every/2 with Process.spawn/4. See it hexdoc of it: https://hexdocs.pm/pelemay_fp/PelemayFp.ParallelSplitter.html#split/7