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

["Ryan S. Arnold" <ryan dot arnold at gmail dot com>]

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 ÂTulio Magno Quites Machado Filho Â<tuliom@linux.vnet.ibm.com>
>
> Â Â Â Â* sysdeps/unix/sysv/linux/powerpc/sys/user.h (__ppc_get_timebase): New
> Â Â Â Âfunction definition.
> Â Â Â Â* sysdeps/unix/sysv/linux/powerpc/Makefile (tests): Add
> Â Â Â Âtest-gettimebase.
> Â Â Â Â* sysdeps/unix/sysv/linux/powerpc/test-gettimebase.c: Test for
> Â Â Â Â__ppc_get_timebase() to catch future ISA opcode/insn changes.
> ---
> Âsysdeps/unix/sysv/linux/powerpc/Makefile      |  Â2 +
> Âsysdeps/unix/sysv/linux/powerpc/sys/user.h     |  38 +++++++++++++++++++-
> Âsysdeps/unix/sysv/linux/powerpc/test-gettimebase.c | Â 37 +++++++++++++++++++
> Â3 files changed, 76 insertions(+), 1 deletions(-)
> Âcreate 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
> Âifeq ($(subdir),elf)
> Âsysdep_routines += dl-vdso
> Âendif
> +
> +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.
> Â ÂThis file is part of the GNU C Library.
>
> Â ÂThe GNU C Library is free software; you can redistribute it and/or
> @@ -36,4 +36,40 @@ struct user {
>    Âchar      Âu_comm[32];       /* user command name */
> Â};
>
> +typedef unsigned long long int __ppc_timebase;
> +
> +/* Read the Time Base Register
> + Â The Time Base Register is a 64-bit register that stores a monotonically
> + Â incremented value updated at a system dependent frequency that may be
> + Â different of processor frequency.
> + Â More information in Power ISA 2.06b - Book II - Section 5.2 Â */
> +#ifdef __powerpc64__
> +static inline __ppc_timebase
> +__ppc_get_timebase (void)
> +{
> + Â__ppc_timebase __tb;
> + Â__asm__ volatile (
> + Â Â Â Â Â Â Â Â Â "mfspr %[tb], 268\n"
> + Â Â Â Â Â Â Â Â Â : [tb]"=r" (__tb)
> + Â Â Â Â Â Â Â Â Â : );
> + Âreturn __tb;
> +}
> +#else Â/* not __powerpc64__ */
> +static inline __ppc_timebase
> +__ppc_get_timebase (void)
> +{
> + Âregister unsigned long __tbu, __tbl, __tmp; \
> + Â__asm__ volatile (
> + Â Â Â Â Â Â Â Â Â "0:\n"
> + Â Â Â Â Â Â Â Â Â "mftbu %[tbu]\n"
> + Â Â Â Â Â Â Â Â Â "mftbl %[tbl]\n"
> + Â Â Â Â Â Â Â Â Â "mftbu %[tmp]\n"
> + Â Â Â Â Â Â Â Â Â "cmpw %[tbu], %[tmp]\n"
> + Â Â Â Â Â Â Â Â Â "bne- 0b\n"
> + Â Â Â Â Â Â Â Â Â : [tbu]"=r" (__tbu), [tbl]"=r" (__tbl), [tmp]"=r" (__tmp)
> + Â Â Â Â Â Â Â Â Â : );
> + Âreturn (( (__ppc_timebase) __tbu << 32) | __tbl);
> +}
> +#endif Â/* not __powerpc64__ */
> +
> Â#endif Â/* 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.
> + Â This file is part of the GNU C Library.
> + Â Contributed by Tulio Magno Quites Machado <tuliom@linux.vnet.ibm.com>, 2012.
> +
> + Â The GNU C Library is free software; you can redistribute it and/or
> + Â modify it under the terms of the GNU Lesser General Public
> + Â License as published by the Free Software Foundation; either
> + Â version 2.1 of the License, or (at your option) any later version.
> +
> + Â The GNU C Library is distributed in the hope that it will be useful,
> + Â but WITHOUT ANY WARRANTY; without even the implied warranty of
> + Â MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. ÂSee the GNU
> + Â Lesser General Public License for more details.
> +
> + Â You should have received a copy of the GNU Lesser General Public
> + Â License along with the GNU C Library; if not, write to the Free
> + Â Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
> + Â 02111-1307 USA. Â*/
> +
> +/* Test if __PPC_GETTIMEBASE() is compatible with the current processor.
> + Â In case of failure it may indicate a future Power ISA or a binutils
> + Â change. Â*/
> +
> +#include <stdio.h>
> +
> +#include <sys/user.h>
> +
> +static int
> +do_test(void)
> +{
> + Â__ppc_timebase tb = __ppc_get_timebase ();
> + Âprintf ("Time Base = %llx\n", tb);
> + Âreturn 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