Re: [Boost-build] BBv2 intolerably slow in Boost tree.

From: David Abrahams (dave_at_[hidden])
Date: 2006-07-27 18:39:27

Vladimir Prus <ghost_at_[hidden]> writes:

> On Thursday 27 July 2006 18:10, David Abrahams wrote:
>> Vladimir Prus <ghost_at_[hidden]> writes:
>> > On Wednesday 26 July 2006 23:20, David Abrahams wrote:
>> >> >> >> > Also, can you try the attached patch to top-level Jamfile.v2?
>> >> >> >>
>> >> >> >> With the patch, it flies!
>> >> >> >
>> >> >> > What's performance of V1? I can replace the globbing code with that
>> >> >> > we have there, as a quick solution.
>> >> >>
>> >> >> v1 is much faster than v2, even with the patch.
>> >> >
>> >> > Then there's something wrong in globbing code.
>> >>
>> >> What makes you think all the time is going into globbing?
>> >
>> > You reported that my patch improves performance considerably. The only
>> > thing the patch does is removing globbing code.
>>
>> Yes, but even with the globbing removed, v2 is still considerably
>> slower than v1.  That suggests to me that there is a culprit other
>> than globbing.  What am I missing?
>
I said
>> >> >> v1 is much faster than v2, even with the patch.

> Hmm, let's go back: I said:
>>
>> >> > Then there's something wrong in globbing code.

"Then... x" implies that x is a consequence of what comes immediately
before.  I don't see how v1 being much faster than v2 with globbing
disabled leads you to the conclusion "there's something wrong in
globbing code."

> to which you replied:
>
>> >> What makes you think all the time is going into globbing?
>
> I did not say that *all* of V2 runtime goes into globbing, and that by 
> removing globbing we can make V2 run in 0 seconds all projects on
> any kind.

Of course I don't think you said that.

> But if removing code that consists only of globbing makes big difference in 
> performance, it means that globbing code is somehow wrong. 

Yes, it does.  But the information "removing code that consists only
of globbing makes big difference in performance" was not what came
immediately before your conclusion.  The information immediately
before your conclusion was "even after you make that big difference,
v2 is still much slower."

> What am I missing?

I hope this clears it up for you.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com