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

[Kristof Beyls via llvm-dev]

FWIW - the patch to record the hash of binaries from the test-suite
into the LNT database has finally landed yesterday, see r249026, r249034,
r249035.

So far, LNT only records the hash data into its database, but doesn't use
it in any analysis or chart yet.
If you upgrade your instance of LNT now, hashes will start being recorded.
Future uses of these hashes in LNT analyses will be able to make use of
historical hashes from the point in time you've started using the now
top-of-trunk LNT.

One idea on how to use the data, next to the automatic noise analysis
algorithm, is to color the background of charts based on the hash value,
so that it's immediately visible for which time periods the binary remained
the same. At least for the sparklines on the daily report page, this
shouldn't be too hard to do.

We ought to also upgrade the instance of LNT running at llvm.org/perf,
but I'm still a bit confused over who knows how to do that? Tanya or
Daniel, could you do that?

Thanks,

Kristof

> -----Original Message-----
> From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu]
> On Behalf Of Chris Matthews
> Sent: 21 May 2015 19:25
> To: Renato Golin
> Cc: LLVM Developers Mailing List
> Subject: Re: [LLVMdev] Proposal: change LNT's regression detection
> algorithm and how it is used to reduce false positives
> 
> 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.
> 
> 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?  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?
> 
> > 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
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