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

Tue Jun 2 18:04:37 PDT 2015

On Tue, Jun 2, 2015 at 2:24 PM, Philip Reames <listmail at philipreames.com>
wrote:

>  Personally, I would prefer this either live in it's own repository, or
> llvm/tools/.  None of my use cases will likely involve the test-suite.
>
> p.s. If this is going to end up an llvm tool, it will need to follow LLVM
> style.
>
> p.p.s. We should probably start a new thread with the proposed addition
> since I imagine many folks are ignoring this one by now given how deep it's
> gotten.
>

Maybe just putting it on github for now is easiest to at least make it
generally available for review. If we later want to officially pull it in
or integrate it with our build system we can do that.

-- Sean Silva

>
>
> Philip
>
>
> On 06/02/2015 12:04 PM, Chris Matthews wrote:
>
> I like that idea!
>
>
>   On Jun 2, 2015, at 12:00 PM, Smith, Kevin B <kevin.b.smith at intel.com>
> wrote:
>
>   The code for cmpimage and getdep consists of five source files, with
> the following sizes
>
>
>
> $ wc *
>
>   5912  20353 191869 cmpimage.cpp
>
>    290   1328  10668 elf.h
>
>   1496   5006  41691 getdep.cpp
>
>    233    959   7692 macho.h
>
>    403   1831  18394 pecoff.h
>
>   8334  29477 270314 total
>
>
>
> to build each of them is just a simple compilation for whatever C++
> compiler you happen to be using (clang, icc, cl, g++)
>
>
>
> $(CXX) –o cmpimage –O2 cmpimage.cpp
>
> $(CXX) –o getdep –O2 getdep.cpp
>
>
>
> This seems like it would fit rather easily into test-suite/tools, which
> already exists and has a Makefile that the commands to build
>
> these could be integrated into.
>
>
>
> This is my best guess/opinion based on a cursory look over the test-suite
> directory structure.
>
>
>
> Kevin
>
>
>
>
>
> *From:* Chris Matthews [mailto:chris.matthews at apple.com
> <chris.matthews at apple.com>]
> *Sent:* Thursday, May 28, 2015 1:02 PM
> *To:* Smith, Kevin B
> *Cc:* Philip Reames; Sean Silva; LLVM Developers Mailing List
> *Subject:* Re: [LLVMdev] Proposal: change LNT’s regression detection
> algorithm and how it is used to reduce false positives
>
>
>
> Where is the best place to keep this?
>
>
>
> - As third party tool we all use?
>
> - Contribute as new project?
>
> - Lives in test-suite/utils?
>
> - Lives in llvm/utils?
>
>
>
>  On May 28, 2015, at 11:22 AM, Smith, Kevin B <kevin.b.smith at intel.com>
> wrote:
>
>
>
> OK, there is interest from at least a couple of people.  What should next
> steps be?
>
>
>
> Kevin
>
>
>
> *From:* Chris Matthews [mailto:chris.matthews at apple.com
> <chris.matthews at apple.com>]
> *Sent:* Thursday, May 28, 2015 10:57 AM
> *To:* Philip Reames
> *Cc:* Smith, Kevin B; Sean Silva; 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. I think there are a lot of exciting uses for this tool.  A stage
> 3 build bot would be another one.
>
>
>
>  On May 28, 2015, at 10:14 AM, Philip Reames <listmail at philipreames.com>
> wrote:
>
>
>
> I'd love to see this tool contributed, even it isn't used for regression
> detection work.  I've got a couple of hacked up scripts which do similar
> things and having a robust tool available for this would be very useful.
>
> Philip
>
> On 05/26/2015 09:53 AM, Smith, Kevin B wrote:
>
> Intel has a binary comparator tool that we have been using for several
> years for comparing output binaries
>
> to see if the code within them is considered identical.  We use it to
> eliminate runs (and therefore some performance noise)
>
> from our own performance tracking tools.
>
>
>
> We are willing to contribute the source code for this to the LLVM
> community if there is interest.
>
>
>
> There are two programs involved:  getdep, which displays the list of
> DLL/.so dependencies of the image in question, and cmpimage itself, which
> does the comparison ignoring the parts not contributed by the compiler.
> The cmpimage program is also almost completely derived from the published
> object format descriptions.
>
>
>
> Let me know if there is interest in these pieces of tooling, and if so,
> what you think next steps should be.
>
>
>
> Kevin B. Smith
>
>
>
> *From:* llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu
> <llvmdev-bounces at cs.uiuc.edu>] *On Behalf Of *Sean Silva
> *Sent:* Thursday, May 21, 2015 2:14 PM
> *To:* Chris Matthews
> *Cc:* LLVM Developers Mailing List
> *Subject:* Re: [LLVMdev] Proposal: change LNT’s regression detection
> algorithm and how it is used to reduce false positives
>
>
>
>
>
>
>
> 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
>
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