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Re: HOWTO: benchmarking monotone (was Re: [Monotone-devel] "memory exhau
From: |
Eric Anderson |
Subject: |
Re: HOWTO: benchmarking monotone (was Re: [Monotone-devel] "memory exhausted" error for 'mtn list status' command) |
Date: |
Fri, 28 Jul 2006 17:21:06 -0700 |
Nathaniel Smith writes:
> On Fri, Jul 28, 2006 at 11:58:29AM -0700, Eric Anderson wrote:
> > avg resident size has decreased from 4.35 to 3.1
> > MiB, avg size has decreased from 21.4 MiB to 19.8 MiB. Similar on the
> > maximum values. The only odd thing is that all three "after" runs
> > took way more wall clock time, but similar system and user time.
>
> Hrm, weird -- I actually re-ran these when writing the email, since
> I'd deleted my first run, and I could swear the numbers were weirder
> before :-). (Weirder, like, swap the average resident sizes between
> the two runs.) I still have some trouble interpreting these -- why are
> the max-resident sizes the same?
I would imagine because there is some point in time where both
processes have the same resident size; it could be at the beginning
Botan does a remarkable amount of self-testing on every run.
> I would have thought that was the
> most interesting number, since peak memory usage is often more
> important than average memory usage, and the total (as opposed to
> resident) numbers are clearly counting, like, the size of all linked
> libraries or something.
> Probably I/we just need more experience in interpreting these numbers;
> they're a little trickier to understand than I expected. (It might
> still be interesting to add an instrumenter that hooks into malloc and
> gives peak _heap_ amounts in particular, just because those are
> presumably less noisy and easier to interpret in terms of code.)
The memtime program is doing sampling of the values in /proc to figure
out how much memory is used at any particular time. This means that
it can miss very short peaks. In general I ignore differences of <
10%, so would have considered the two runs you had to be pretty much
the same, even though there is a valid statistical difference on both
the avg-{resident,size} and max-size. That said a resident size of
<10MB is pretty much nothing.
-Eric