i586+ implementation of clock_settime.
authordrepper <drepper>
Sat, 21 Apr 2001 07:43:02 +0000 (07:43 +0000)
committerdrepper <drepper>
Sat, 21 Apr 2001 07:43:02 +0000 (07:43 +0000)
sysdeps/unix/i386/i586/clock_settime.c [new file with mode: 0644]

diff --git a/sysdeps/unix/i386/i586/clock_settime.c b/sysdeps/unix/i386/i586/clock_settime.c
new file mode 100644 (file)
index 0000000..465a68f
--- /dev/null
@@ -0,0 +1,85 @@
+/* Copyright (C) 2001 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
+   modify it under the terms of the GNU Library General Public License as
+   published by the Free Software Foundation; either version 2 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
+   Library General Public License for more details.
+
+   You should have received a copy of the GNU Library General Public
+   License along with the GNU C Library; see the file COPYING.LIB.  If not,
+   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+   Boston, MA 02111-1307, USA.  */
+
+#include <time.h>
+
+#include "cpuclock-init.h"
+
+
+/* This implementation uses the TSC register in modern (i586 and up) IA-32
+   processors (most modern clones also provide it).  Since we need the
+   resolution of the clock and since determining this is not cheap, we
+   cache the value.  But this means that systems with processors running
+   at different speeds or process migration to machines with slower or
+   faster processors will not work without changes.  */
+
+
+/* Clock frequency of the processor.  We make it a 64-bit variable
+   because some jokers are already playing with processors with more
+   than 4GHz.  */
+static unsigned long long int freq;
+
+
+/* We need the starting time for the process.  */
+CPUCLOCK_VARDECL (_dl_cpuclock_offset);
+
+
+/* This function is defined in the thread library.  */
+extern void __pthread_clock_settime (unsigned long long int offset)
+     __attribute__ ((__weak__));
+
+
+/* We add an limitation here: we assume that the process is not
+   running as long as it takes to wrap-around the 64-bit timestamp
+   counter.  On a 4GHz machine it would take 136 years of uptime to
+   wrap around so this "limitation" is not severe.  */
+#define EXTRA_CLOCK_CASES \
+  case CLOCK_PROCESS_CPUTIME_ID:                                             \
+  case CLOCK_THREAD_CPUTIME_ID:                                                      \
+    {                                                                        \
+      unsigned long long int tsc;                                            \
+      unsigned long long int usertime;                                       \
+                                                                             \
+      /* First thing is to get the current time.  */                         \
+      asm volatile ("rdtsc" : "=A" (tsc));                                   \
+                                                                             \
+      if (__builtin_expect (freq == 0, 0))                                   \
+       {                                                                     \
+         /* This can only happen if we haven't initialized the `freq'        \
+            variable yet.  Do this now. We don't have to protect this        \
+            code against multiple execution since all of them should         \
+            lead to the same result.  */                                     \
+         freq = __get_clockfreq ();                                          \
+         if (__builtin_expect (freq == 0, 0))                                \
+           /* Something went wrong.  */                                      \
+           break;                                                            \
+       }                                                                     \
+                                                                             \
+      /* Convert the user-provided time into CPU ticks.  */                  \
+      usertime = tp->tv_sec * freq + (tp->tv_nsec * freq) / 1000000000ull;    \
+                                                                             \
+      /* Determine the offset and use it as the new base value.  */          \
+      if (clock_id != CLOCK_THREAD_CPUTIME_ID                                \
+         || __pthread_clock_settime == NULL)                                 \
+       _dl_cpuclock_offset = tsc - usertime;                                 \
+      else                                                                   \
+       __pthread_clock_settime (tsc - usertime);                             \
+    }                                                                        \
+  break;
+
+#include <sysdeps/unix/clock_settime.c>