Re: cost of -MP

[Noel Yap]

Boris Kolpackov wrote:

> Noel Yap <address@hidden> writes:
>
> > Interesting, non-recursive was slower than recursive.  I suppose I can see 
> > this happening if there weren't that many directories in the project.  How 
> > many directories do you have?
>
> It is 19 make re-executions. The reason non-recursive is slower is that I 
> haven't had a chance to optimize it yet. I actually expect it to be faster 
> than recursive (for obvious reasons). 

It just occurred to me:

If the re-exec's are occurring due to the dependencies file generation, then 
converting to the more advanced way of generating dependencies files will 
eliminate the 19 re-exec's.

So, try to optimize away the re-exec's first (this should be the most bang for 
the buck), then redo the timings.  My guess is that the differences will 
dwindle a lot.

Otherwise, if you're running on Linux, try running Valgrind to see where the 
slowdown is.

Noel