Re: Compiler performance tests on FreeBSD 10.0-CURRENT

On Wed, Sep 05, 2012 at 03:13:11PM -0700, Steve Kargl wrote:
> On Wed, Sep 05, 2012 at 11:31:26AM +0200, Dimitry Andric wrote:
> > On 2012-09-05 01:40, Garrett Cooper wrote:
> > ...
> > >     Steve does have a point. Posting the results of
> > >CFLAGS/CPPFLAGS/LDFLAGS/etc for config.log (and maybe poking through
> > >the code to figure out what *FLAGS were used elsewhere) is more
> > >valuable than the data is in its current state (unfortunately..
> > >autoconf makes things more complicated).
> > 
> > 1) For building the FreeBSD in-tree version of clang 3.2:
> > 
> >      -O2 -pipe -fno-strict-aliasing
> > 
> > 2) For building the FreeBSD in-tree version of gcc 4.2.1:
> > 
> >      -O2 -pipe
> > 
> > 3) For building Boost 1.50.0:
> > 
> >      -ftemplate-depth-128 -O3 -finline-functions
> > 
> 
> Dimitry thanks for the follow-up.  I performed an unscientific
> (micro)benchmark of /usr/bin/cc vs /usr/bin/clang where cc is
> the base system's gcc 4.2.1.  Here's what I found/feared.
> 
> Compiling libm on 
> 
> CPU: AMD Opteron(tm) Processor 248 (2192.01-MHz K8-class CPU)
>   Origin = "AuthenticAMD"  Id = 0xf5a  Family = f  Model = 5  Stepping = 10
>   Features=0x78bfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,\
>                      MCA,CMOV,PAT,PSE36,CLFLUSH,MMX,FXSR,SSE,SSE2>
>   AMD Features=0xe0500800<SYSCALL,NX,MMX+,LM,3DNow!+,3DNow!>
> 
> with default CFLAGS (ie., -O2 -pipe) and -march=opteron.
 
Was this compiled as amd64 or i386? Also, can you send me the test case?
So that we can explore the difference. The working theory now is SSE vs FPU
mathematics, but it would be nice to see the testcase.

Thank you, roman

> Using 'setenv CC /usr/bin/cc' with 3 runs of
> 
> make clean
> time make -DNO_MAN
> 
> yields
> 
>        69.39 real        52.00 user        38.55 sys
>        69.57 real        52.35 user        38.37 sys
>        69.48 real        52.25 user        38.38 sys
> 
> Now, repeating with 'setenv CC /usr/bin/clang' yields
> 
>        39.65 real        21.86 user        17.37 sys
>        40.91 real        21.48 user        17.91 sys
>        39.77 real        21.65 user        17.64 sys
> 
> So, clang does appear to be faster in this particular 
> compiling speed benchmark.
> 
> However, if I know build my test program for libm's j0f()
> function where the only difference is whether libm was
> built with /usr/bin/cc or /usr/bin/clang, I observe the
> following results. 
>                      
> 1234567 x values in the interval [0:25]    
> 
>                          gcc libm    |   clang libm
>                      ----------------|-----------------
>       ULP <= 0.6 --> 565515 (45.81%) | 513763 (41.61%)
> 0.6 < ULP <= 0.7 --> 74148  ( 6.01%) | 67221  ( 5.44%)
> 0.7 < ULP <= 0.8 --> 69112  ( 5.60%) | 62846  ( 5.09%)
> 0.8 < ULP <= 0.9 --> 63798  ( 5.17%) | 58217  ( 4.72%)
> 0.9 < ULP <= 1.0 --> 58679  ( 4.75%) | 53834  ( 4.36%)
> 1.0 < ULP <= 2.0 --> 328221 (26.59%) | 306728 (24.84%)
> 2.0 < ULP <= 3.0 --> 65323  ( 5.29%) | 63452  ( 5.14%)
> 3.0 < ULP        --> 9771   ( 0.79%) | 108506 ( 8.79%)
> 
>                     gcc libm         |     clang libm
>               -----------------------|--------------------
>      MAX ULP: 12152.27637            | 1129606938624.00000
> x at MAX ULP: 5.520077 0x1.6148f2p+2 | 2.404833 0x1.33d19p+1
> 
> Speed test with gcc libm.
> 1234567 j0f calls in 0.193427 seconds.
> 1234567 j0f calls in 0.193410 seconds.
> 1234567 j0f calls in 0.194158 seconds.
> 
> Speed test with clang libm.
> 1234567 j0f calls in 0.180260 seconds.
> 1234567 j0f calls in 0.180130 seconds.
> 1234567 j0f calls in 0.179739 seconds.
> 
> So, although the clang built j0f() appears to be faster than
> the gcc built j0f(), the clang built j0f() has much worse
> accuracy issues.
> 
> -- 
> Steve
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