On Tue, Apr 26, 2016 at 11:33 AM, Heckendorn, Robert (hecke...@uidaho.edu) < hecke...@uidaho.edu> wrote:
> What kind of performance difference does that make? Why not O3?
>
That is a very good question that requires a "scientific" answer! I decided
to run Unicon benchmarks (run-benchmark level) and see what I get at
different optimization levels, here are the results:
Compared to the base level (no optimizations -O0) here are the net gains
for the different optimization levels:
-O1 41%
-O2 69%
-O3 73%
-O2 compared to -O1: 20%
-O3 compared to -O2: 2%
-O3 was almost identical to -O2 in all tests (few percents above or below)
There was one test (chameneos-redux, a concurrent tests) where -O2
performed
badly even worse than -O1 (compared to base: -O1 gave 35%, -O2 gave 18%,
-O3 gave 39% ). The 2% advantage of -O3 over -O2 above was largely due to
this test.
Conclusions 1: There is no reason not to turn on optimization, -O2 at
least,
the gains are significant.
Conclusion 2: chameneos-redux should be a case study to find out what
is going on at -O2
Disclaimer: The current benchmarks set don't cover all language features so
depending on your specific use case, your mileage may
vary :-)
The full details of the tests/timings can be found in the attached Excel
sheet.
Cheers,
Jafar
>
> thanks,
>
> > On Apr 26, 2016, at 8:25 AM, Jafar Al-Gharaibeh <to.ja...@gmail.com>
> wrote:
> >
> > Hi,
> >
> > C Compiler optimizations (-O2) flag has been added to the default
> build. We dropped -O2 a few years back from the default configuration after
> reports that it caused issues on some platforms. We believe that we
> addressed the problem (by another compiler flag :)) and it is now safe to
> leave it on.
> >
> > Concurrency has also been turned on by default (if pthread library is
> detected). If you don't want concurrent threads, please add the following
> line to your define.h:
> >
> > #define NoConcurrent
> >
> > Cheers,
> > Jafar
> >
> >
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>
> ------------------------------------------------------------------------------
> |
> | "The belief that there is only one truth, and that oneself is in
> | possession of it, is the root of all evil in the world." -- Max
> Born
> |
> | Dr. Robert Heckendorn
> | hecke...@uidaho.edu
> | http://marvin.cs.uidaho.edu/~heckendo
> | Computer Science Dept, Univ. of Idaho, Moscow, Idaho, USA 83844-1010
>
>
Optimized-Unicon.xlsx
Description: MS-Excel 2007 spreadsheet
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