Re: [DynInst_API:] DynInst Overhead

[Bill Williams <bill@xxxxxxxxxxx>]

On 07/21/2014 11:52 AM, Matthew LeGendre wrote:
> Presumably you're running the CodeCoverage tool in two steps: 1)
> Rewriting the binary 2) Running the rewritten binary.  All of the
> analysis/rewriting overheads are in step 1, and the instrumentation
> overhead can be measured just by timing step 2.
>
> If you're getting 50x overhead on just step 2 then something's very
> wrong. I've got my own codeCoverage tool (which I unfortunately can't
> share yet) and I only see 10% overhead.
Hrm. If this is with a prebuilt, statically linked binary and not with a 
build from source against current Dyninst, we may also be hitting traps 
in an inner loop. That's more the right order of magnitude than 
trampguards would be--trampguards would be in the 1.5-5x sort of 
neighborhood off the top of my head.
The source for CodeCoverage (which you can build against the latest 
Dyninst and be reasonably sure of *not* hitting traps in almost all of 
SPEC) is in our tools.git repository. I know we've fixed some 
performance regressions that turned up between the AWAT paper and 8.1.2.
> Just an educated guess--I frequently see big overheads associated with
> trampoline guards.  Dyninst should have realized trampoline guards are
> unnecessary for codeCoverage and not emited them.  But if something went
> wrong you can manually turn them off by putting a call to:
>
>    bpatch.setTrampRecursive(true);
>
> Near the top of codeCoverage.C's main() function.  If that makes a
> difference then let the list know.  That implies there's a bug that
> should be investigated.
>
> -Matt
>
>
> On Mon, 21 Jul 2014, Buddhika Chamith Kahawitage Don wrote:
> > I just measured the time it took for a single run. Is there a way to
> > get the
> > time it took for initialization only so that I can get an idea of just
> > the
> > run-time overhead?
> >
> > Thanks
> > Bud
> >
> >
> > On Mon, Jul 21, 2014 at 7:58 AM, Frank Ch. Eigler <fche@xxxxxxxxxx>
> > wrote:
> >       Hi -
> >
> >       > [...]  I was using the CodeCoverage tool [2] for
> >       > instrumentation. But it's taking way too higher time than the
> > > unprofiled run. (More than a 50x slow down) [...]
> >
> > Are you measuring steady-state overheads only, or else are you
> > including the one-time analysis too?  The latter can be quite
> > large, but you pay it only once per startup.
> >
> > - FChE
>
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--
--bw

Bill Williams
Paradyn Project
bill@xxxxxxxxxxx