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Re: [PATCH] PowerPC - Add a faster way to read the Time Base register
- From: Richard Henderson <rth at twiddle dot net>
- To: Tulio Magno Quites Machado Filho <tuliom at linux dot vnet dot ibm dot com>
- Cc: libc-alpha at sourceware dot org
- Date: Tue, 14 Feb 2012 12:03:06 -0800
- Subject: Re: [PATCH] PowerPC - Add a faster way to read the Time Base register
- References: <1329233454-15224-1-git-send-email-tuliom@linux.vnet.ibm.com>
On 02/14/2012 07:30 AM, Tulio Magno Quites Machado Filho wrote:
> Add macro __PPC_GETTIMEBASE() 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.
>
> My FSF copyright assignment is on file.
>
> 2012-02-06 Tulio Magno Quites Machado Filho <tuliom@linux.vnet.ibm.com>
>
> * sysdeps/unix/sysv/linux/powerpc/sys/user.h: New macro definition.
> * sysdeps/unix/sysv/linux/powerpc/Makefile (tests): Add
> test-gettimebase.
> * sysdeps/unix/sysv/linux/powerpc/test-gettimebase.c: Test for
> __PPC_GETTIMEBASE() to catch future ISA opcode/insn changes.
> ---
> sysdeps/unix/sysv/linux/powerpc/Makefile | 2 +
> sysdeps/unix/sysv/linux/powerpc/sys/user.h | 40 +++++++++++++++++++-
> sysdeps/unix/sysv/linux/powerpc/test-gettimebase.c | 35 +++++++++++++++++
> 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..301e64a 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 +36,42 @@ struct user {
> char u_comm[32]; /* user command name */
> };
>
> +typedef unsigned long long int __ppc_timebase;
> +
> +#define __STRINGIFY(...) #__VA_ARGS__
> +#define STRINGIFY(...) __STRINGIFY(__VA_ARGS__)
> +
> +#define SPRN_TBRL 268 /* Time Base Read Lower Register */
> +
> +#ifdef __powerpc64__
> +# define __PPC_GETTIMEBASE() \
> + ({ \
> + __ppc_timebase __tb; \
> + __asm__ volatile ( \
> + "mfspr %[tb], " STRINGIFY(SPRN_TBRL) "\n" \
Is there a good reason why you're stringify-ing this constant
rather than just writing "mfspr %0, 268"? You certainly don't
want to be polluting the namespace with an unadorned "STRINGIFY".
Is there a good reason this is a macro rather than an inline?
r~