maria-developers team mailing list archive

[Michael Widenius <monty@xxxxxxxxxxxx>]

Hi!

>>>>> "knielsen" == knielsen  <knielsen@xxxxxxxxxxxxxxx> writes:

knielsen> #At lp:maria
knielsen>  2703 knielsen@xxxxxxxxxxxxxxx	2009-06-10
knielsen>       Fix XtraDB to build with atomic operations, for good performance.
      
knielsen>       The root of the problem is that ./configure mixed together two different things. One is the
knielsen>       availability of GCC atomic operation intrinsics. The other is the selection of which
knielsen>       primitives to use for my_atomic implementation.
      
knielsen>       Then at some point a hack was made to not use GCC intrinsics in my_atomic to work around
knielsen>       some test failures. But because the two things are mixed in ./configure, this as a side
knielsen>       effect also makes GCC intrinsics unavailable for XtraDB.
      
knielsen>       Fixed by splitting this in two in configure, so that we have HAVE_GCC_ATOMIC_BUILTINS for
knielsen>       GCC intrinsics availability and MY_ATOMIC_MODE_GCC_BUILTINS for use in my_atomic.
knielsen>       modified:
knielsen>         configure.in
knielsen>         include/atomic/nolock.h

knielsen> === modified file 'configure.in'
knielsen> --- a/configure.in	2009-04-23 13:06:16 +0000
knielsen> +++ b/configure.in	2009-06-10 09:13:53 +0000
knielsen> @@ -1726,6 +1726,30 @@ then
knielsen>    fi
knielsen>  fi
 
knielsen> +AC_CACHE_CHECK([whether the compiler provides atomic builtins],
knielsen> +	       [mysql_cv_gcc_atomic_builtins], [AC_TRY_RUN([
knielsen> +  int main()
knielsen> +  {
knielsen> +    int foo= -10; int bar= 10;
knielsen> +    if (!__sync_fetch_and_add(&foo, bar) || foo)
knielsen> +      return -1;
knielsen> +    bar= __sync_lock_test_and_set(&foo, bar);
knielsen> +    if (bar || foo != 10)
knielsen> +      return -1;
knielsen> +    bar= __sync_val_compare_and_swap(&bar, foo, 15);
knielsen> +    if (bar)
knielsen> +      return -1;
knielsen> +    return 0;
knielsen> +  }
knielsen> +], [mysql_cv_gcc_atomic_builtins=yes],
knielsen> +   [mysql_cv_gcc_atomic_builtins=no],
knielsen> +   [mysql_cv_gcc_atomic_builtins=no])])
knielsen> +
knielsen> +if test "x$mysql_cv_gcc_atomic_builtins" = xyes; then
knielsen> +  AC_DEFINE(HAVE_GCC_ATOMIC_BUILTINS, 1,
knielsen> +	    [Define to 1 if compiler provides atomic builtins.])
knielsen> +fi
knielsen> +
knielsen>  AC_ARG_WITH([atomic-ops],
knielsen>  	    AC_HELP_STRING([--with-atomic-ops=rwlocks|smp|up],
knielsen>  	    [Implement atomic operations using pthread rwlocks or atomic CPU
knielsen> @@ -1739,28 +1763,9 @@ case "$with_atomic_ops" in
knielsen>                    [Use pthread rwlocks for atomic ops]) ;;
knielsen>    "smp") ;;
knielsen>    "")
knielsen> -    AC_CACHE_CHECK([whether the compiler provides atomic builtins],
knielsen> -                   [mysql_cv_gcc_atomic_builtins], [AC_TRY_RUN([
knielsen> -      int main()
knielsen> -      {
knielsen> -        int foo= -10; int bar= 10;
knielsen> -        if (!__sync_fetch_and_add(&foo, bar) || foo)
knielsen> -          return -1;
knielsen> -        bar= __sync_lock_test_and_set(&foo, bar);
knielsen> -        if (bar || foo != 10)
knielsen> -          return -1;
knielsen> -        bar= __sync_val_compare_and_swap(&bar, foo, 15);
knielsen> -        if (bar)
knielsen> -          return -1;
knielsen> -        return 0;
knielsen> -      }
knielsen> -    ], [mysql_cv_gcc_atomic_builtins=yes_but_disabled],
knielsen> -       [mysql_cv_gcc_atomic_builtins=no],
knielsen> -       [mysql_cv_gcc_atomic_builtins=no])])
knielsen> -
knielsen> -    if test "x$mysql_cv_gcc_atomic_builtins" = xyes; then
knielsen> -      AC_DEFINE(HAVE_GCC_ATOMIC_BUILTINS, 1,
knielsen> -                [Define to 1 if compiler provides atomic builtins.])
knielsen> +    if test "x$mysql_cv_gcc_atomic_builtins" = xyes_but_disabled; then
knielsen> +      AC_DEFINE([MY_ATOMIC_MODE_GCC_BUILTINS], [1],
knielsen> +                [Use GCC atomic builtins for atomic ops])

<cut>

Under which circumstances could the last 'if' be true?  The new code
don't seem to be able to set mysql_cv_gcc_atomic_builtins to
yes_but_disabled which makes the last if always false and we never
define MY_ATOMIC_MODE_GCC_BUILTINS as 1.

Regards,
Monty