Question

Lecture chapter 12 by Erik通过引入示例函数sumWith来提及“改善空间使用”。

我代表懒惰版和严格版，如下所示。

sumWith1 v [] = v
sumWith1 v (x:xs) = sumWith1 (v+x) xs

sumWith2 v [] = v
sumWith2 v (x:xs) = (sumWith2 $! (v+x)) xs

test = sumWith1 0 [1..200000000]

我认为严格版本应该在一定程度上提高性能我尝试验证杠杆GHC分析工具。

$ ghc --make -O2 -prof -auto-all -rtsopts -o test1
$ ./test1 +RTS -p -RTS

在sumWith1函数下将sumWith2更改为test，然后再次执行test2。

以下是分析结果：http://pastie.org/4720019。

通过查看%alloc列，我看不出这两个函数之间的差异。

我的问题是如何改进测试用例以找到一些区别。换句话说，是否可以为这种情况分析空间使用情况？

谢谢。

Answer 1

使用GHC的堆分析器。

在RWH, ch25中详细描述。这是a fully worked example。

Answer 2

以下是您的计划统计数据（我已将上限减少到1000000）

这是你修改过的程序

sumWith1 v [] = v
sumWith1 v (x:xs) = sumWith1 (v+x) xs

sumWith2 v [] = v
sumWith2 v (x:xs) = (sumWith2 $! (v+x)) xs

main = print $ sumWith1 0 [1..1000000]

使用ghc -prof -fprof-auto -rtsopts heap.hs

进行编译

对于sumwith1

./heap +RTS -sstderr -K500M
500000500000
     266,384,496 bytes allocated in the heap
     367,442,520 bytes copied during GC
     117,747,616 bytes maximum residency (8 sample(s))
       1,931,472 bytes maximum slop
             196 MB total memory in use (0 MB lost due to fragmentation)

                                    Tot time (elapsed)  Avg pause  Max pause
  Gen  0       393 colls,     0 par    0.19s    0.19s     0.0005s    0.0455s
  Gen  1         8 colls,     0 par    0.20s    0.21s     0.0257s    0.0832s

  INIT    time    0.00s  (  0.00s elapsed)
  MUT     time    0.15s  (  0.16s elapsed)
  GC      time    0.39s  (  0.39s elapsed)
  RP      time    0.00s  (  0.00s elapsed)
  PROF    time    0.00s  (  0.00s elapsed)
  EXIT    time    0.00s  (  0.00s elapsed)
  Total   time    0.55s  (  0.55s elapsed)

  %GC     time      71.2%  (71.5% elapsed)

  Alloc rate    1,689,230,189 bytes per MUT second

  Productivity  28.7% of total user, 28.7% of total elapsed

对于sumwith2

./heap +RTS -sstderr -K500M           
500000500000
     256,057,488 bytes allocated in the heap
          65,256 bytes copied during GC
          30,240 bytes maximum residency (1 sample(s))
          21,440 bytes maximum slop
               1 MB total memory in use (0 MB lost due to fragmentation)

                                    Tot time (elapsed)  Avg pause  Max pause
  Gen  0       488 colls,     0 par    0.00s    0.00s     0.0000s    0.0000s
  Gen  1         1 colls,     0 par    0.00s    0.00s     0.0003s    0.0003s

  INIT    time    0.00s  (  0.00s elapsed)
  MUT     time    0.14s  (  0.14s elapsed)
  GC      time    0.00s  (  0.00s elapsed)
  RP      time    0.00s  (  0.00s elapsed)
  PROF    time    0.00s  (  0.00s elapsed)
  EXIT    time    0.00s  (  0.00s elapsed)
  Total   time    0.14s  (  0.14s elapsed)

  %GC     time       1.8%  (1.8% elapsed)

  Alloc rate    1,798,840,354 bytes per MUT second

  Productivity  98.0% of total user, 99.3% of total elapsed

您可以看到GC数量和使用的总内存之间的巨大差异。有关更多信息，请参阅Don指出的RWH章节。

是否可以在Haskell中分析空间使用情况

2 个答案: