OpenBLAS/GotoBLAS_03FAQ.txt

	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