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GotoBLAS_03FAQ.txt
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GotoBLAS_03FAQ.txt
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GotoBLAS2 FAQ
1. General
1.1 Q Can I find useful paper about GotoBLAS2?
A You may check following URL.
http://www.cs.utexas.edu/users/flame/Publications/index.htm
11. Kazushige Goto and Robert A. van de Geijn, " Anatomy of
High-Performance Matrix Multiplication," ACM Transactions on
Mathematical Software, accepted.
15. Kazushige Goto and Robert van de Geijn, "High-Performance
Implementation of the Level-3 BLAS." ACM Transactions on
Mathematical Software, submitted.
1.2 Q Does GotoBLAS2 work with Hyperthread (SMT)?
A Yes, it will work. GotoBLAS2 detects Hyperthread and
avoid scheduling on the same core.
1.3 Q When I type "make", following error occured. What's wrong?
$shell> make
"./Makefile.rule", line 58: Missing dependency operator
"./Makefile.rule", line 61: Need an operator
...
A This error occurs because you didn't use GNU make. Some binary
packages install GNU make as "gmake" and it's worth to try.
1.4 Q Function "xxx" is slow. Why?
A Generally GotoBLAS2 has many well optimized functions, but it's
far and far from perfect. Especially Level 1/2 function
performance depends on how you call BLAS. You should understand
what happends between your function and GotoBLAS2 by using profile
enabled version or hardware performance counter. Again, please
don't regard GotoBLAS2 as a black box.
1.5 Q I have a commercial C compiler and want to compile GotoBLAS2 with
it. Is it possible?
A All function that affects performance is written in assembler
and C code is just used for wrapper of assembler functions or
complicated functions. Also I use many inline assembler functions,
unfortunately most of commercial compiler can't handle inline
assembler. Therefore you should use gcc.
1.6 Q I use OpenMP compiler. How can I use GotoBLAS2 with it?
A Please understand that OpenMP is a compromised method to use
thread. If you want to use OpenMP based code with GotoBLAS2, you
should enable "USE_OPENMP=1" in Makefile.rule.
1.7 Q Could you tell me how to use profiled library?
A You need to build and link your application with -pg
option. After executing your application, "gmon.out" is
generated in your current directory.
$shell> gprof <your application name> gmon.out
Each sample counts as 0.01 seconds.
% cumulative self self total
time seconds seconds calls Ks/call Ks/call name
89.86 975.02 975.02 79317 0.00 0.00 .dgemm_kernel
4.19 1020.47 45.45 40 0.00 0.00 .dlaswp00N
2.28 1045.16 24.69 2539 0.00 0.00 .dtrsm_kernel_LT
1.19 1058.03 12.87 79317 0.00 0.00 .dgemm_otcopy
1.05 1069.40 11.37 4999 0.00 0.00 .dgemm_oncopy
....
I think profiled BLAS library is really useful for your
research. Please find bottleneck of your application and
improve it.
1.8 Q Is number of thread limited?
A Basically, there is no limitation about number of threads. You
can specify number of threads as many as you want, but larger
number of threads will consume extra resource. I recommend you to
specify minimum number of threads.
1.9 Q I have segfaults when I compile with USE_OPENMP=1. What's wrong?
A This may be related to a bug in the Linux kernel 2.6.32. Try applying
the patch segaults.patch using
patch < segfaults.patch
and see if the crashes persist. Note that this patch will lead to many
compiler warnings.
2. Architecture Specific issue or Implementation
2.1 Q GotoBLAS2 seems to support any combination with OS and
architecture. Is it possible?
A Combination is limited by current OS and architecture. For
examble, the combination OSX with SPARC is impossible. But it
will be possible with slight modification if these combination
appears in front of us.
2.2 Q I have POWER architecture systems. Do I need extra work?
A Although POWER architecture defined special instruction
like CPUID to detect correct architecture, it's privileged
and can't be accessed by user process. So you have to set
the architecture that you have manually in getarch.c.
2.3 Q I can't create DLL on Cygwin (Error 53). What's wrong?
A You have to make sure if lib.exe and mspdb80.dll are in Microsoft
Studio PATH. The easiest way is to use 'which' command.
$shell> which lib.exe
/cygdrive/c/Program Files/Microsoft Visual Studio/VC98/bin/lib.exe