Profiling semantics

Roman Cheplyaka roma at
Tue Jan 17 12:02:48 CET 2012

* Simon Marlow <marlowsd at> [2012-01-17 09:44:22+0000]
> On 17/01/2012 09:30, Roman Cheplyaka wrote:
> >* Simon Marlow<marlowsd at>  [2012-01-03 11:00:58+0000]
> >>I'd be interested in hearing feedback, particularly if you find a
> >>case where costs are attributed somewhere that you didn't expect, or
> >>the stack looks wrong.
> >
> >What I often find counter-intuitive is how the 'entries' count is
> >computed.
> >
> >Sometimes I see 0 entries for some SCC while its children have non-zero
> >entries counts. I guess this has to do with inlining? Still, I don't see
> >why it should be so -- if it's possible to compute metrics like time and
> >allocations for such an SCC, why shouldn't it be possible to compute
> >entries?
> >
> >Another case is when a function has a large number of entries, although
> >in reality it's entered only once (I can confirm that using trace, for
> >example). My guess would be that its SCC got inherited by some recursive
> >function, but again, this is very confusing.
> >
> >And because of things like that, I don't usually trust the entries
> >counts even when they look realistic.
> >
> >I observe this with GHC 7.0.3. Do you think this was improved in GHC
> >7.4.1?
> This is improved a *lot* with 7.4.1.  In fact, we know for sure that
> it was completely broken before that.  Please try with 7.4.1 and let
> me know if you still find anything strange.

Sounds great, thanks!

Roman I. Cheplyaka ::

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