hp-timing.h

glibc2.5版源代码

/* High precision, low overhead timing functions.  powerpc64 version.
   Copyright (C) 2005 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Ulrich Drepper <[e-mail]>, 1998.

   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.  */

#ifndef _HP_TIMING_H
#define _HP_TIMING_H	1

#include <string.h>
#include <sys/param.h>
#include <stdio-common/_itoa.h>
#include <atomic.h>

/* The macros defined here use the powerpc 64-bit time base register.
   The time base is nominally clocked at 1/8th the CPU clock, but this
   can vary.

   The list of macros we need includes the following:

   - HP_TIMING_AVAIL: test for availability.

   - HP_TIMING_INLINE: this macro is non-zero if the functionality is not
     implemented using function calls but instead uses some inlined code
     which might simply consist of a few assembler instructions.  We have to
     know this since we might want to use the macros here in places where we
     cannot make function calls.

   - hp_timing_t: This is the type for variables used to store the time
     values.

   - HP_TIMING_ZERO: clear `hp_timing_t' object.

   - HP_TIMING_NOW: place timestamp for current time in variable given as
     parameter.

   - HP_TIMING_DIFF_INIT: do whatever is necessary to be able to use the
     HP_TIMING_DIFF macro.

   - HP_TIMING_DIFF: compute difference between two times and store it
     in a third.  Source and destination might overlap.

   - HP_TIMING_ACCUM: add time difference to another variable.  This might
     be a bit more complicated to implement for some platforms as the
     operation should be thread-safe and 64bit arithmetic on 32bit platforms
     is not.

   - HP_TIMING_ACCUM_NT: this is the variant for situations where we know
     there are no threads involved.

   - HP_TIMING_PRINT: write decimal representation of the timing value into
     the given string.  This operation need not be inline even though
     HP_TIMING_INLINE is specified.

*/

/* We always assume having the timestamp register.  */
#define HP_TIMING_AVAIL		(1)

/* We indeed have inlined functions.  */
#define HP_TIMING_INLINE	(1)

/* We use 64bit values for the times.  */
typedef unsigned long long int hp_timing_t;

/* Set timestamp value to zero.  */
#define HP_TIMING_ZERO(Var)	(Var) = (0)

/* That's quite simple.  Use the `mftb' instruction.  Note that the value
   might not be 100% accurate since there might be some more instructions
   running in this moment.  This could be changed by using a barrier like
   'lwsync' right before the `mftb' instruciton.  But we are not interested
   in accurate clock cycles here so we don't do this.  */
#define HP_TIMING_NOW(Var)	__asm__ __volatile__ ("mftb %0" : "=r" (Var))

/* Use two 'mftb' instructions in a row to find out how long it takes.
   On current POWER4, POWER5, and 970 processors mftb take ~10 cycles.  */
#define HP_TIMING_DIFF_INIT() \
  do {									      \
    if (GLRO(dl_hp_timing_overhead) == 0)				      \
      {									      \
	int __cnt = 5;							      \
	GLRO(dl_hp_timing_overhead) = ~0ull;				      \
	do								      \
	  {								      \
	    hp_timing_t __t1, __t2;					      \
	    HP_TIMING_NOW (__t1);					      \
	    HP_TIMING_NOW (__t2);					      \
	    if (__t2 - __t1 < GLRO(dl_hp_timing_overhead))		      \
	      GLRO(dl_hp_timing_overhead) = __t2 - __t1;		      \
	  }								      \
	while (--__cnt > 0);						      \
      }									      \
  } while (0)

/* It's simple arithmetic in 64-bit.  */
#define HP_TIMING_DIFF(Diff, Start, End)	(Diff) = ((End) - (Start))

/* We need to insure that this add is atomic in threaded environments.  We use
   __arch_atomic_exchange_and_add_64 from atomic.h to get thread safety.  */
#define HP_TIMING_ACCUM(Sum, Diff) \
  do {									      \
    hp_timing_t __diff = (Diff) - GLRO(dl_hp_timing_overhead);		      \
    __arch_atomic_exchange_and_add_64 (&(Sum), __diff);	                      \
  } while (0)

/* No threads, no extra work.  */
#define HP_TIMING_ACCUM_NT(Sum, Diff)	(Sum) += (Diff)

/* Print the time value.  */
#define HP_TIMING_PRINT(Buf, Len, Val) \
  do {									      \
    char __buf[20];							      \
    char *__cp = _itoa (Val, __buf + sizeof (__buf), 10, 0);		      \
    size_t __len = (Len);						      \
    char *__dest = (Buf);						      \
    while (__len-- > 0 && __cp < __buf + sizeof (__buf))		      \
      *__dest++ = *__cp++;						      \
    memcpy (__dest, " ticks", MIN (__len, sizeof (" ticks")));  \
  } while (0)

#endif	/* hp-timing.h */