Re: Mainline mt_allocator performance on sparc-sun-solaris2.8

[Brad Spencer <spencer at infointeractive dot com>]

On Mon, Sep 13, 2004 at 12:15:13PM -0500, Benjamin Kosnik wrote:
> 
> >This is slower than gcc-3.4.1.  Percentage difference between each
> >slot on the gcc-3.4.1 table and gcc-4.0.0 table:
> >
> >        -4.867% -15.324% -8.733% -15.224% -13.925% -2.035%
> >        -4.995%  -4.872% -7.592%  -9.126%  -3.582% -6.545%
> >        -11.423% -6.209%  9.218%  -5.644% --3.759% -0.530%
> >
> >This seems fairly significant to me.
> 
> I see this too. If you switch from __common_pool_policy to
> __per_type_pool_policy it should go away, due to improved inlining.

Ahh, by using __mt_alloc<type, __per_type_pool_policy>, I suppose.  
Hmmmm... I'm not sure how practical this will be unless I can easily
configure the compiler with that as the default allocator.  

> I'd
> like to elaborate on this, but before I do can I get your test program?
> I don't see it in any of the posts.

Yes, of course.  It was depending on some support libraries, but
I've separated the essence of the timing test and made it standalone.
Sorry for it being a bit sloppy, but it's attached.  Oh, and there's
no deep theoretical basis for the algorithm :)  I'm just trying to
similate _some_ usage to get a metric.

It's using clock_gettime() for the timing, so on Linux, add -lt, and
on Solaris, add -lposix4.  There is no good reason for this. 

> You can force single threaded behavior, even from threads enabled
> configs in the current mt_alloc sources.

Gotcha.  I still think it's odd that the performance hit would be so
dramatic just by using the thread-aware pool.  Here are some new runs
with the attached standalone test.  The compiler is the same and the
configure options are the same except for the --enable-threads
selection.

Configured with: ../../gcc-4.0.0/configure --with-dwarf2 --enable-languages=c,c++ --enable-threads=yes --disable-shared --prefix=/hosts/bubbles/spencer/devel/gcc/install-threaded/gcc-4.0.0-cross/sparc-sun-solaris2.8 --with-gnu-as --with-gnu-ld --disable-multilib --enable-concept-checks --enable-clocale=generic --enable-libstdcxx-allocator=mt --target=sparc-sun-solaris2.8 --with-sysroot=/opt/sysroot/sparc-sun-solaris2.8/
Thread model: posix
gcc version 4.0.0 20040912 (experimental)

                        Number of slots
Size             1       8      64    1024    8192 1048576
---------- ------- ------- ------- ------- ------- -------
   8 bytes 0.65408 0.74944 0.83358 0.74248 0.76384 0.79638
 128 bytes 0.75224 0.88115  1.0066 0.92986  1.0087  1.0435
1024 bytes 0.89352  0.9052 0.91799 0.90635 0.90713  1.2161

Configured with: ../../gcc-4.0.0/configure --with-dwarf2 --enable-languages=c,c++ --enable-threads=no --disable-shared --prefix=/hosts/bubbles/spencer/devel/gcc/install/gcc-4.0.0-cross/sparc-sun-solaris2.8 --with-gnu-as --with-gnu-ld --disable-multilib --enable-concept-checks --enable-clocale=generic --enable-libstdcxx-allocator=mt --target=sparc-sun-solaris2.8 --with-sysroot=/opt/sysroot/sparc-sun-solaris2.8/
Thread model: single
gcc version 4.0.0 20040912 (experimental)

                        Number of slots
Size             1       8      64    1024    8192 1048576
---------- ------- ------- ------- ------- ------- -------
   8 bytes  2.4847  2.1741  2.3043  2.1742  1.9974  1.9253
 128 bytes  3.5108  3.0202  2.9637  2.5956  2.6348   2.205
1024 bytes 0.87176 0.90735 0.94823 0.93351 0.94565  1.1434

I profiled the theaded version, and it's showing the top three
"non-framework" functions as

  __gnu_cxx::__pool<(bool)1>::_M_reclaim_memory(char*, unsigned)
  __gnu_cxx::__mt_alloc<char, __gnu_cxx::__common_pool_policy<(bool)1> >::allocate(unsigned, void const*)
  __gnu_cxx::__pool<(bool)1>::_M_get_thread_id()

[BTW, thanks for pointing out that those were forward declarations in
the other post ;)  Doh!]

-- 
------------------------------------------------------------------
Brad Spencer - spencer@infointeractive.com - "It's quite nice..."
Systems Architect | InfoInterActive Corp. | A Canadian AOL Company

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