英文:
Cost centres for Generic-derived instances?
问题
根据+RTS -p所继承的时间，我的执行时间的90%用于运行基于Generic的instance MyClass MyType定义，递归地针对100多个类型/实例运行一次类。我已经尝试让GHC告诉我这些细节，以找出哪些实例较慢，或哪些实例被更频繁地调用，以便我可以手动优化它们。
然而，即使使用-fprof-auto-calls，我似乎无法让GHC在这些函数上放置成本中心。
我该怎么做才能在每个类型类实例函数上获得调用中心，而不仅仅是整个顶层内容，以便我知道在每个实例中花费了多少时间？
使用GHC 9.2.4。
英文:
According to +RTS -p time inherited, 90% of my execution time is spent running a Generic based instance MyClass MyType definitions, for a single class recursively over 100+ types/instances. I've tried getting GHC to tell me the details of that, to figure out which instances are slow, or which instances are called more often, so I can go and hand-optimize those.
However, I can't seem to get ghc to put cost centres on these functions even with -fprof-auto-calls.
What can I do to get call centres on each type class instance function, rather than just the whole top-level thing as one, so I know how much time is spent in each one?
Using ghc 9.2.4.
答案1
得分: 1
以下是翻译好的部分：
如果您有一个典型的通用函数设置，其中包括用于处理表示的类，其实例执行所有实际工作：
class GSlow f where
gslow :: f a -> Int
一个独立的类型类用于通用函数本身：
class Slow a where
slow :: a -> Int
default slow :: (Generic a, GSlow (Rep a)) => a -> Int
slow = defaultSlow
defaultSlow :: (Generic a, GSlow (Rep a)) => a -> Int
defaultSlow = gslow . from
用于将控制从一个数据类型传递到另一个数据类型的K1字段的实例：
instance Slow c => GSlow (K1 i c) where
gslow (K1 x) = ... slow x ...
以及一堆空实例用于您的100+数据类型：
instance Slow Type1
instance Slow Type2
等等
然后，最简单的方法是使用搜索和替换将空的instance Slow替换为：
instance Slow Type1 where slow = defaultSlow
instance Slow Type2 where slow = defaultSlow
使用-fprof-auto，您应该为每个类型特定的slow = defaultSlow函数获得一个调用中心，这将使您能够将GSlow实例中的工作归因于各个数据类型。
英文:
If you have a typical generic function setup with a class for processing the representation whose instances do all the actual work:
class GSlow f where
gslow :: f a -> Int
a separate type class for the generic function itself:
class Slow a where
slow :: a -> Int
default slow :: (Generic a, GSlow (Rep a)) => a -> Int
slow = defaultSlow
defaultSlow :: (Generic a, GSlow (Rep a)) => a -> Int
defaultSlow = gslow . from
an instance for fields K1 that passes control from one data type to the other:
instance Slow c => GSlow (K1 i c) where
gslow (K1 x) = ... slow x ...
and a whole bunch of empty instances for your 100+ data types:
instance Slow Type1
instance Slow Type2
etc.
then, by far, the easiest thing to do is to search and replace your empty instance Slows with:
instance Slow Type1 where slow = defaultSlow
instance Slow Type2 where slow = defaultSlow
With -fprof-auto, you should get a call center for every type-specific slow = defaultSlow function which should allow you to attribute the work in the GSlow instances to individual data types.
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