[PATCHv2] PowerPC - Add a faster way to read the Time Base register

[Ryan S. Arnold]

On Wed, Feb 22, 2012 at 11:49 AM, Tulio Magno Quites Machado Filho
<tuliom@linux.vnet.ibm.com> wrote:
> Add function __ppc_get_timebase() to directly read the Time Base register.
> This is required for applications that measure time at high frequencies
> with high precision that can't afford a syscall.
>
> 2012-02-17  Tulio Magno Quites Machado Filho  <tuliom@linux.vnet.ibm.com>
>
>        * sysdeps/unix/sysv/linux/powerpc/sys/user.h (__ppc_get_timebase): New
>        function definition.
>        * sysdeps/unix/sysv/linux/powerpc/Makefile (tests): Add
>        test-gettimebase.
>        * sysdeps/unix/sysv/linux/powerpc/test-gettimebase.c: Test for
>        __ppc_get_timebase() to catch future ISA opcode/insn changes.
> ---
>  sysdeps/unix/sysv/linux/powerpc/Makefile           |    2 +
>  sysdeps/unix/sysv/linux/powerpc/sys/user.h         |   38 +++++++++++++++++++-
>  sysdeps/unix/sysv/linux/powerpc/test-gettimebase.c |   37 +++++++++++++++++++
>  3 files changed, 76 insertions(+), 1 deletions(-)
>  create mode 100644 sysdeps/unix/sysv/linux/powerpc/test-gettimebase.c
>
> diff --git a/sysdeps/unix/sysv/linux/powerpc/Makefile b/sysdeps/unix/sysv/linux/powerpc/Makefile
> index 55311a4..a2ab09a 100644
> --- a/sysdeps/unix/sysv/linux/powerpc/Makefile
> +++ b/sysdeps/unix/sysv/linux/powerpc/Makefile
> @@ -15,3 +15,5 @@ endif
>  ifeq ($(subdir),elf)
>  sysdep_routines += dl-vdso
>  endif
> +
> +tests += test-gettimebase
> diff --git a/sysdeps/unix/sysv/linux/powerpc/sys/user.h b/sysdeps/unix/sysv/linux/powerpc/sys/user.h
> index 5fa3745..d26c70b 100644
> --- a/sysdeps/unix/sysv/linux/powerpc/sys/user.h
> +++ b/sysdeps/unix/sysv/linux/powerpc/sys/user.h
> @@ -1,4 +1,4 @@
> -/* Copyright (C) 1998 Free Software Foundation, Inc.
> +/* Copyright (C) 1998, 2012 Free Software Foundation, Inc.
>    This file is part of the GNU C Library.
>
>    The GNU C Library is free software; you can redistribute it and/or
> @@ -36,4 +36,40 @@ struct user {
>        char            u_comm[32];             /* user command name */
>  };
>
> +typedef unsigned long long int __ppc_timebase;
> +
> +/* Read the Time Base Register
> +   The Time Base Register is a 64-bit register that stores a monotonically
> +   incremented value updated at a system dependent frequency that may be
> +   different of processor frequency.
> +   More information in Power ISA 2.06b - Book II - Section 5.2   */
> +#ifdef __powerpc64__
> +static inline __ppc_timebase
> +__ppc_get_timebase (void)
> +{
> +  __ppc_timebase __tb;
> +  __asm__ volatile (
> +                   "mfspr %[tb], 268\n"
> +                   : [tb]"=r" (__tb)
> +                   : );
> +  return __tb;
> +}
> +#else  /* not __powerpc64__ */
> +static inline __ppc_timebase
> +__ppc_get_timebase (void)
> +{
> +  register unsigned long __tbu, __tbl, __tmp; \
> +  __asm__ volatile (
> +                   "0:\n"
> +                   "mftbu %[tbu]\n"
> +                   "mftbl %[tbl]\n"
> +                   "mftbu %[tmp]\n"
> +                   "cmpw %[tbu], %[tmp]\n"
> +                   "bne- 0b\n"
> +                   : [tbu]"=r" (__tbu), [tbl]"=r" (__tbl), [tmp]"=r" (__tmp)
> +                   : );
> +  return (( (__ppc_timebase) __tbu << 32) | __tbl);
> +}
> +#endif  /* not __powerpc64__ */
> +
>  #endif  /* sys/user.h */
> diff --git a/sysdeps/unix/sysv/linux/powerpc/test-gettimebase.c b/sysdeps/unix/sysv/linux/powerpc/test-gettimebase.c
> new file mode 100644
> index 0000000..90b207b
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/powerpc/test-gettimebase.c
> @@ -0,0 +1,37 @@
> +/* Copyright (C) 2012 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +   Contributed by Tulio Magno Quites Machado <tuliom@linux.vnet.ibm.com>, 2012.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, write to the Free
> +   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
> +   02111-1307 USA.  */
> +
> +/* Test if __PPC_GETTIMEBASE() is compatible with the current processor.
> +   In case of failure it may indicate a future Power ISA or a binutils
> +   change.  */
> +
> +#include <stdio.h>
> +
> +#include <sys/user.h>
> +
> +static int
> +do_test(void)
> +{
> +  __ppc_timebase tb = __ppc_get_timebase ();
> +  printf ("Time Base = %llx\n", tb);
> +  return 0;
> +}
> +
> +#define TEST_FUNCTION do_test ()
> +#include "../test-skeleton.c"
> --
> 1.7.4.4
>

This looks good to me.  I'll commit it in if/when I get an ACK from Richard.

Ryan S. Arnold