[C2hs] Re: [Gtk2hs-users] Profiling c2hs
A.Simon at kent.ac.uk
Wed May 5 10:17:54 EDT 2004
On 5 May 2004, at 06:08, Duncan Coutts wrote:
> I was writing a demo app to add to gtk2hs's small collection; it's a
> viewer for ghc's time profile log files, and I needed a large profile
> file to test it on so I thought I'd try profiling c2hs. Here's what I
> Looking at allocations (which corresponds quite closely with time):
> Note that these are % of the total cost, not % of their parent cost
> 11.7% is taken by the C & chs lexers which is not unreasonable.
> 77.4% is taken by the CParser
> Within the CParser:
> 72.0% is taken by parseCExtDeclList, within which
> 65.5% is taken by morphTypeNames (and 58.2% of the runtime)
> 31.4% alloc & 26.5% time was taken just by calls to Prelude.elem within
> In this particular run of c2hs, in which it was processing some large
> gtk+ headers, it called morphTypeNames over 55 million times.
> I narrowed this down a bit more and found that it is the call to
> morphTypeNames from parseCExtDeclList that takes the time, the call
> parseCHeader is insignificant. Furthermore, it is the recursive calls
> morphTypeNames that is expensive; parseCExtDeclList only called
> morphTypeNames about 1000 times (compared to 55 million recursive
> So what's going and and what can we do?
> If I understand the code correctly, the reason we are doing this
> morphTypeNames is because we can't distinguish typedef'ed identifiers
> the parser, we need to remember which identifiers were typedefs and
> treat them differently in the parser later if they were. At the moment
> this is done by after parsing each declaration (which might contain
> typedefs) modifying the remaining stream of tokens changing all
> identifiers that have been discovered to be typedefs from ordinary
> identifier tokens to typedef-identifier tokens. This is expensive.
> Perhaps it would be possible to add this set of typedef identifiers to
> the parser state monad and thread it through to the parsers for cid and
> typedefName which could consult this parser state and match
> conditionally on the identifier token being in the typedef-identifier
> set or not. (cidOrTN would not need to to a lookup) This would avoid
> traversing the token stream after parsing each declaration.
> Sound reasonable?
It might be worth a shot. Eliminating this function call would
certainly speed up things, however, c2hs seems to be slow due to its
huge memory footprint at runtime which probably doesn't change
(although it might).
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