Development of a performance tracking tool for Mercurial

Mon Jun 27 12:53:17 EDT 2016

> On Jun 27, 2016, at 5:24 AM, Philippe Pepiot <philippe.pepiot at logilab.fr> wrote:
> 
> Hi,
> 
> I rewrote the benchmarks suite (https://hg.logilab.org/review/hgperf <https://hg.logilab.org/review/hgperf>) using contrib/perf.py from tested version of mercurial while keeping old helper functions to write plain benchmarks easily.
> 
> Here is a summary of the current status of the project:
> 
> All my patches are merged upstream into AirSpeed Velocity, especially ordering commit by graph revision instead of date which was the big one.
> I'm running a demo https://jenkins.philpep.org/hgperf/ <https://jenkins.philpep.org/hgperf/> that benchmark all revisions added to the repository since one month, with sparse earlier commits too (since 3.4).
> 
Sweet!
> One interesting result is that I'm benchmarking mercurial against the same mercurial repository, i.e. the reference repository is pulled, this explain all the small detected regressions. So benchmarking a moving repository should be avoided (seems trivial to say but I wasn't sure how this will be visible on the graphs)
> 
Yes, this makes sense. We should probably take a bit of time to define specific repositories as of specific heads for benchmarking (I think we should probably have at least one for each of small, medium, and large?)

> ASV is actively maintained some new features are incoming:
> 
> https://github.com/spacetelescope/asv/pull/447 <https://github.com/spacetelescope/asv/pull/447> Regressions notifications using atom feed, this one is part of the plan. If people prefer to receive notifications via email, there are tools like rss2email or online services to transform new feed items into an email.
> 
> https://github.com/spacetelescope/asv/pull/437 <https://github.com/spacetelescope/asv/pull/437> This one (WIP) is quite interesting because it track improvement too and provide a useful summary page.
> In the plan, https://www.mercurial-scm.org/wiki/PerformanceTrackingSuitePlan <https://www.mercurial-scm.org/wiki/PerformanceTrackingSuitePlan> , the next topic is using unit test execution time as benchmark result and related topics (Annotation system, handle changed tests, scenario based benchmarks). Most of them are shell style (.t) tests that spawn a lot of hg subprocesses and I wonder if it's relevant to use them as benchmark result because they work on very small repositories (generated during tests) and I think most of the time is spent on hg startup. Maybe we could detect startup time regression here, but I think we should miss others regressions that will be insignificant comparing to the whole test duration. I wonder if it's worth to put efforts on this topic, but I maybe missing something, do you have already used unit test execution time to compare performance changes introduced by a commit ?
> 
> Some other topics might require more work, like improving the web interface, for instance having a "per commit" view that summarize regressions and improvements introduced by a single commit, integrate the benchmark suite in mercurial, write more benchmarks, I could start by cover all combination of benchmarks/options offered in contrib/perf.py. Another topic could be extensions benchmarking. I put the development in pause while waiting your feedback, hoping (or not ;)) they will be some real regressions detected soon to validate the tool, I'll add the atom feed once it get merged in ASV.
> Cheers,
> 
> On 05/26/2016 11:57 AM, Philippe Pepiot wrote:
>> 
>> 
>> On 05/23/2016 11:38 PM, Kevin Bullock wrote:
>>> (resurrecting this thread now that I've had a closer look at the plan)
>>> 
>> 
>> Thanks !
>> 
>>>> >On Apr 12, 2016, at 05:03, Philippe Pepiot<philippe.pepiot at logilab.fr> <mailto:philippe.pepiot at logilab.fr>  wrote:
>>>> >
>>>> >[...]
>>>> >Now I've a question about writing and maintaining benchmark code as we have multiple choices here:
>>>> >
>>>> >1) Use mercurial internal API (benefits: unlimited possibilities without modifying mercurial and we can write backward compatible benchmark with some 'if' statements and benchmarks older versions, profits all ASV features (profiling, memory benchmarks etc). Drawbacks: duplicate code with contrib/perf.py, will break on internal API changes, need more maintenance and more code to write/keep backward compatible benchmarks).
>>>> >
>>>> >2) Use contrib/perf.py extension from the benchmarked version of mercurial (benefits: de facto backward compatible, drawbacks: limited to what the tool can do in previous versions)
>>>> >
>>>> >3) Use contrib/perf.py extension from the latest version of mercurial (benefits: no duplicate code, easier maintenance, new benchmarks profits to both tools. Drawbacks: not backward compatible for now (it works only for >= 3.7 versions)). We could also implement some glue code, either in the tracking tool or in contrib/perf.py, to list available benchmarks and theirs parameters.
>>>> >
>>>> >At this stage of the project my advice it to use 1), but we could also have a mix of 1) and 3). It depend on how fast are internal api changes and on your short/mid/long term objectives on the level of integration of the tracking tool.
>>> My first instinct tells me we should use approach #2, and teach the benchmark suite what Mercurial release a given perf* command first appeared in. This can be automated by reading the output of `hg help -e perf`.
>>> 
>>> #1 sounds like a particularly bad idea given the deliberately high level of churn in our internal APIs. If we try to maintain an external tool that also tries to remember the details of that churn, I'm pretty sure it will rot and fall out of use in short order.
>>> 
>>> #3 has a similar (though lesser) disadvantage. I also don't see a strong need to run new perf checks against old versions, with the exception of perhaps the current stable release.
>>> 
>>> All that said, please convince me I'm wrong.:)
>>> 
>>> Regarding ASV: is there any way we can use it to instrument our code (including profiling and memory tracking) without having it call into the internals? Specifically, is there a way that we can either feed it metrics that we output from the perf extension, or integrate it into perf.py such that it gets optionally imported (similar to how you can optionally use ipdb via the --debugger flag, wired up in dispatch.py)?
>> 
>> Ok if the internal API used in perf.py often change we can exclude #1 (at least until the benchmark suite is included into mercurial repository).
>> 
>> Nevertheless #1 can still be useful if you want to bisect a old regression (and have no relevant benchmark code on the bisect range), this can be done by just transforming the perf.py benchmark into a regular asv benchmark (quite easy step), handle potential backward compatibility then run the bisect.
>> 
>> With #2 we cannot fix potential "bugs" in perf.py when benchmarking old revisions. For instance if an internal change alter a benchmark that is no more computing the same thing than above and it's fixed later on, you will keep having wrong values even if you re-run the benchmarks (but this is not a big issue).
>> 
>> About #3, currently perf.py is not backward compatible with < 3.7 versions but it seems related to the extension code (not benchmark code). After embedding commands.formatteropts and commands.debugrevlogopts and remove the norepo parameter from perflrucache, I can run some benchmarks on 3.0 versions.
>> 
>> For now, #2 (and #3) can be achieved with ASV by writing a "track" benchmark that run the given perf.py command in a subprocess and return the value.
>> 
>> To get a closer integration (and enable profiling features of ASV) we could write a module that declare benchmarks (setup code and body code) and let both asv and perf.py use it. Actually asv benchmark themselves could be a candidate because this is just declarative code (functions and class with naming convention and "setup" attribute on the function), there is no dependency on asv here.
>> 
>> Another idea could be to call perf.py commands programmatically in ASV and eventually monkeypatch the gettimer() function to transform the command into a regular asv "time benchmark".
>> 
>> As a first step, I think we can go for the simplest solution (ie. #2) and keep in mind a future inclusion (or dedicated api) in mercurial.
>> 
> 
> --
> Philippe Pepiot
> https://www.logilab.fr <https://www.logilab.fr/>_______________________________________________
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