[llvm-dev] New LLD performance builder

Galina Kistanova via llvm-dev llvm-dev at lists.llvm.org
Fri Feb 16 13:30:16 PST 2018

Hello George,

Sorry, somehow hit a send button too soon. Please ignore the previous

The bot does 10 runs for each of the benchmarks (those dots in the logs are
meaningful). We can increase the number of runs if proven that this would
significantly increase the accuracy. I didn't see the increase in accuracy when
have been staging the bot, which would justify the extra time and larger
gaps between the tested revisions.  10 runs seems give a good balance. But
I'm open for suggestions.

It seems the statistics are quite stable if you would look over number of
And in this particular case the picture seems quite clear.

At http://lnt.llvm.org/db_default/v4/link/104, the list of Performance
Regressions suggests that the most hit was with the linux-kernel. The
regressed metrics - branches, branch-misses, instructions,
cycles, seconds-elapsed, task-clock. Some other benchmarks shows
regressions in branches and branch-misses, some shows improvements.

The metrics are consistent before and after the commit, so, I do not think
this one is an outliner.
For example, if one would take a look at the linux-kernel branches -
it gets obvious that the number of branches increased significantly as a
result of the r325313. The metric is very stable around the impacted commit
and does not go down after. The  branch-misses is more volatile, but still
consistently shows the regression as the result of this commit.

Now someone should see why this particular commit has resulted in
significant increase of branching with the Linux Kernel.

As of how to use LNT web UI, I'm sure you have checked that, but, just in
case, here is the link to the LNT doc - http://llvm.org/docs/lnt/con

> task-clock results are available for "linux-kernel" and "llvm-as-fsds"
only and all other
> tests has blank field. Should it mean there was no noticable difference
in results ?

If you would go to http://lnt.llvm.org/db_default/v4/link/104#task-clock
(or go to  http://lnt.llvm.org/db_default/v4/link/104 and select the task-clock
on the left, which is the same), you would see the list of actual values in
the "Current" column. All of them populated, none is blank. The column "%"
contains the difference from the previous run in percents, or dash for no
measured difference.

>  Also, "Graph" and "Matrix" buttons whatever they should do show errors

I guess you didn't select what to graph or what to show as a matrix, did

Besides reporting to the lnt.llvm.org, each build contains in the log all
the reported data, so you could process it whatever you want and find

Hope this helps.



On Fri, Feb 16, 2018 at 1:55 AM, George Rimar via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> >Hello everyone,
> >
> >I have added a new public LLD performance builder at
> >http://lab.llvm.org:8011/builders/lld-perf-testsuite.
> >It builds LLVM and LLD by the latest releaed Clang and runs a set of
> >perfromance tests.
> >
> >The builder is reliable. Please pay attention on the failures.
> >
> >The performance statistics are here:
> >http://lnt.llvm.org/db_default/v4/link/recent_activity
> >
> >Thanks
> >
> >Galina
> Great news, thanks !
> Looking on results I am not sure how to explain them though.
> For example r325313 fixes "use after free", it should not give any
> performance
> slowdowns or boosts. Though if I read results right, they show 23.65%
> slowdown
> for time of linking linux kernel (http://lnt.llvm.org/db_
> default/v4/link/104).
> I guess such variation can happen for example if bot do only single link
> iteration for tests,
> so that final time is just a error mostly probably.
> task-clock results are available for "linux-kernel" and "llvm-as-fsds"
> only and all other
> tests has blank field. Should it mean there was no noticable difference in
> results ?
> Also, "Graph" and "Matrix" buttons whatever they should do show errors atm.
> ("Nothing to graph." and "Not Found: Request requires some data
> arguments.").
> Best regards,
> George | Developer | Access Softek, Inc
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
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