Please find my responses inline. On Mon, Jul 21, 2014 at 1:48 PM, Bill Williams <b...@cs.wisc.edu> wrote:
> 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. >> > That's true. > >> 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. > In fact that was the use case I had in my mind. But I was just checking the static rewriting case first up since it was readily available with code-coverage tool. > 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. > I am using dyninst 8.1.2 which I built from source. > > >> 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); >> > Tried it without any success :( > >> 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. >> > Any ideas on how to debug this? Thanks Bud
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