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| delaw |
 Posted: Thu Aug 30, 2007 9:39 pm |
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Joined: 30 Aug 2007
Posts: 2
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hello all,
First of all, please excuse me for my english :+)
I'm discovering the erlang language and OTP framework... it's great ! I like it ! It's fun :p
I would like to know how much time took to compute something in my program ?
I use the erlang:now() function before and after an operation, and i compute the difference between the two values.
I take the example from the book "programming erlang"
For example :
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T1 = erlang:now(),
L = for(1,N,fun() -> spawn(fun() -> wait() end) end),
T2 = erlang:now(),
Diff = timer:now_diff(T2,T1),
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The now_diff function return the time elapsed between T2 and T1.
But in the book "programmin erlang" (always the same, the bible ? ) the author used :
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erlang:statistics(runtime),
erlang:statistics(wall_clock),
L = for(1,N,fun() -> spawn(fun() -> wait() end) end),
{_,Time1} = erlang:statistics(runtime),
{_,Time2} = erlang:statistics(wall_clock),
U1 = Time1 * 1000 / N,
U2 = Time2 * 1000 / N,
io:format("Process spawn time= ~p (~p) microseconds~n",[U1,U2]).
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The results are realy different if i use a method or the other.
Someone could explain me this difference ?
Thank you for your help.
delaw |
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| michal |
| Posted: Fri Aug 31, 2007 5:33 pm |
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User
Joined: 20 Jul 2006
Posts: 44
Location: London
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Hi,
erlang:statistics/1 function returns time in milliseconds and then this value is multiplied by 1000 to get the time in microseconds. One of the reasons why you get different results could be related to this rounding.
erlang:statistics/1 function returns time since last call of this function with a particular parameter. What is the difference between runtime and wall_clock parameter? runtime indicates how long CPU was busy with your task only. If during execution of your task there were some other tasks that the CPU was busy with, then the wall_clock time will be higher than the runtime time. I would assume that wall_clock time is not very much different from what you get using erlang:now() function.
Michal |
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http://www.erlang-consulting.com |
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| Mazen |
| Posted: Tue Sep 04, 2007 8:50 am |
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User
Joined: 20 Jul 2006
Posts: 164
Location: London
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Small tip:
If you want to know the time it took to run a function but also want to retrieve the result of that function in one go then consider using: timer:tc/3
It will return a tuple of {Time, Value} where the Time is the time it took to run in microseconds and Value is the return value of the function.
/Mazen
1) http://www.erlang.org/doc/man/timer.html |
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| delaw |
| Posted: Sat Sep 08, 2007 9:13 am |
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Joined: 30 Aug 2007
Posts: 2
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Thank you for your responses.
delaw |
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