functional again

Joachim Breitner mail at
Tue Oct 24 15:14:44 UTC 2017


Am Dienstag, den 24.10.2017, 16:59 +0200 schrieb Boespflug, Mathieu:
> Hi Joachim,
> > But that’s what I am saying: By measuring dynamic instructions (using
> > cachegrind), the execution time is no longer relevant.
> I'm skeptical that this metric is a reliable enough proxy for actual
> runtime of user programs to make tracking it and only it sufficient.
> For the reasons Sven Panne gave in a previous email. But I'll be very
> interested to hear your experience report over time.

Sure, it’s a crutch. But we have been working for decades with
“allocations go down, so this must be a win”, which is even more
distant from runtime.

If someone builds me a system where the runtime measurements are
actually reliable (and not drowned in the noise of modern CPU
architectures with sensitivity to layout and alignment), maybe using a
tool like this
then I’ll happily ditch instruction counts and use that!

But at the current state, working with nofib results is just too
frustrating: You see a change, but you don't know, is it a measurement
error? Did you push something over a performance cliff? Is it really
related to your change to Core? I find it just not viable.


Joachim Breitner
  mail at
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