[LLVMdev] Proposal: change LNT’s regression detection algorithm and how it is used to reduce false positives

[Sean Silva]

On Thu, May 21, 2015 at 11:24 AM, Chris Matthews <chris.matthews at apple.com>
wrote:

> I agree this is a great idea.  I think it needs to be fleshed out a little
> though.
>
> It would still be wise to run the regression detection algorithm, because
> the test suite changes and the machines change, and the algorithm is not
> perfect yet.  It would be a valuable source of information though.
>

How would running it as part of regular testing change anything? Presumably
the only purpose it would serve is retrospectively going back and seeing
false-positives in the aggregate. But if we are already doing offline
analysis, we can run the regression detection algorithm (or any prospective
ones) offline on the raw data; it doesn't take that long.


>
> This is not a small change to how LNT works, so I think some due diligence
> is necessary.  Is clang *really* that deterministic, especially over
> successive revs?


Yes. Actually, google's build system depends on this for its caching
strategy to work and so the google guys are usually on top of any issues in
this respect (thanks google guys!).



> I know it is supposed to be.  Does anyone have any data to show this is
> going to be an effective approach?  It seems like there are benchmarks in
> the test-suite which use __DATE__ and __TIME__ in them. I assume that will
> be a problem?
>

__DATE__ and __TIME__ should be easy to solve by modifying the benchmark,
or teaching clang to always return a fixed value for them (maybe we already
have this? IIRC google's build system does something like this; or maybe
the do it at the OS level).

-- Sean Silva


>
> > On May 21, 2015, at 1:43 AM, Renato Golin <renato.golin at linaro.org>
> wrote:
> >
> > On 20 May 2015 at 23:31, Sean Silva <chisophugis at gmail.com> wrote:
> >> In the last 10,000 revisions of LLVM+Clang, only 10 revisions actually
> >> caused the binary of MultiSource/Benchmarks/BitBench/five11 to change.
> So if
> >> just store a hash of the binary in the database, we should be able to
> pool
> >> all samples we have collected while the binary is the the same as it
> >> currently is, which will let us use significantly more datapoints for
> the
> >> reference.
> >
> > +1
> >
> >
> >> Also, we can trivially eliminate running the regression detection
> algorithm
> >> if the binary hasn't changed.
> >
> > +2!
> >
> > --renato
> > _______________________________________________
> > LLVM Developers mailing list
> > LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150521/39198687/attachment.html>