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Rate limit expensive _SC_NPROCESSORS_ONLN computation

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Ulrich Drepper 2011-06-22 09:50:39 -04:00
parent 6e502e1945
commit 852eb34d5c
2 changed files with 36 additions and 1 deletions
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5
ChangeLog
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@ -1,3 +1,8 @@
2011-06-22 Ulrich Drepper <drepper@gmail.com>
* sysdeps/unix/sysv/linux/getsysstats.c (__get_nprocs): Rate limit
reading the information from the /proc filesystem to once a second.
2011-06-21 Andreas Jaeger <aj@suse.de>
* sysdeps/unix/sysv/linux/bits/sigcontext.h: Fix definition of

32
sysdeps/unix/sysv/linux/getsysstats.c
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@ -1,5 +1,5 @@
/* Determine various system internal values, Linux version.
Copyright (C) 1996-2003,2006,2007,2009,2010 Free Software Foundation, Inc.
Copyright (C) 1996-2003,2006,2007,2009,2010,2011 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Ulrich Drepper <drepper@cygnus.com>, 1996.
@ -35,6 +35,16 @@
#include <atomic.h>
#include <not-cancel.h>
#include <kernel-features.h>
#ifndef HAVE_CLOCK_GETTIME_VSYSCALL
# undef INTERNAL_VSYSCALL
# define INTERNAL_VSYSCALL INTERNAL_SYSCALL
# undef INLINE_VSYSCALL
# define INLINE_VSYSCALL INLINE_SYSCALL
#else
# include <bits/libc-vdso.h>
#endif
/* How we can determine the number of available processors depends on
@ -128,6 +138,22 @@ next_line (int fd, char *const buffer, char **cp, char **re,
int
__get_nprocs ()
{
static int cached_result;
static time_t timestamp;
#ifdef __ASSUME_POSIX_TIMERS
struct timespec ts;
INTERNAL_SYSCALL_DECL (err);
INTERNAL_VSYSCALL (clock_gettime, err, 2, CLOCK_REALTIME, &ts);
#else
struct timeval ts;
gettimeofday (&ts, NULL);
#endif
time_t prev = timestamp;
atomic_read_barrier ();
if (ts.tv_sec == prev)
return cached_result;
/* XXX Here will come a test for the new system call. */
const size_t buffer_size = __libc_use_alloca (8192) ? 8192 : 512;
@ -169,6 +195,10 @@ __get_nprocs ()
}
}
cached_result = result;
atomic_write_barrier ();
timestamp = ts.tv_sec;
return result;
}
weak_alias (__get_nprocs, get_nprocs)