From: Andreas Jaeger <aj@suse.de>
To: Glibc hackers <libc-hacker@sources.redhat.com>
Subject: Re: get_nprocs question
Date: Tue, 16 Mar 2004 20:05:00 -0000 [thread overview]
Message-ID: <m3d67ch817.fsf@gromit.moeb> (raw)
In-Reply-To: <m3brmxia3m.fsf@gromit.moeb> (Andreas Jaeger's message of "Tue, 16 Mar 2004 07:23:25 +0100")
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Andreas Jaeger <aj@suse.de> writes:
> What exactly is the semantics of get_nprocs, the manual states:
> The @code{get_nprocs} function returns the number of available processors.
>
> Does available mean the number of all processors the kernel runs on?
> Or does it mean the number of CPUs upon which the process and its
> children will be permitted to execute?
>
> In the latter case we can use the sched_getaffinity system call for
> get_nprocs if it's available. If this is ok, I'll prepare a patch...
Here's the proposed patch. Is this ok?
Andreas
2004-03-16 Andreas Jaeger <aj@suse.de>
Andi Kleen <ak@suse.de>
* sysdeps/unix/sysv/linux/getsysstats.c (popcnt): New.
(__get_nprocs): Use sched_getaffinity to get number of processors.
============================================================
Index: sysdeps/unix/sysv/linux/getsysstats.c
--- sysdeps/unix/sysv/linux/getsysstats.c 4 Sep 2003 08:25:11 -0000 1.27
+++ sysdeps/unix/sysv/linux/getsysstats.c 16 Mar 2004 20:04:23 -0000
@@ -1,5 +1,5 @@
/* Determine various system internal values, Linux version.
- Copyright (C) 1996-2001, 2002, 2003 Free Software Foundation, Inc.
+ Copyright (C) 1996-2001, 2002, 2003, 2004 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Ulrich Drepper <drepper@cygnus.com>, 1996.
@@ -133,6 +133,26 @@ get_proc_path (char *buffer, size_t bufs
while (0)
#endif
+static unsigned char pop4 [16] =
+{
+ 0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4
+};
+
+/* Population count: count number of bits set. */
+static int
+popcnt (unsigned char *buffer, int num)
+{
+ int count = 0;
+ int i;
+ for (i = 0; i < num; i++)
+ {
+ unsigned char w = buffer[i];
+ count += pop4[w >> 4] + pop4[w & 0xF];
+ }
+ return count;
+}
+
+
int
__get_nprocs ()
{
@@ -141,7 +161,17 @@ __get_nprocs ()
const char *proc_path;
int result = 1;
- /* XXX Here will come a test for the new system call. */
+#ifdef __NR_sched_getaffinity
+ cpu_set_t cpuset;
+
+ result = INLINE_SYSCALL (sched_getaffinity, 3, __getpid(), sizeof (cpu_set_t),
+ &cpuset);
+ if (result != -1)
+ {
+ return popcnt ((unsigned char *) &cpuset, result);
+ }
+
+#endif
/* Get mount point of proc filesystem. */
proc_path = get_proc_path (buffer, sizeof buffer);
--
Andreas Jaeger, aj@suse.de, http://www.suse.de/~aj
SuSE Linux AG, Maxfeldstr. 5, 90409 Nürnberg, Germany
GPG fingerprint = 93A3 365E CE47 B889 DF7F FED1 389A 563C C272 A126
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next prev parent reply other threads:[~2004-03-16 20:05 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-03-16 6:23 Andreas Jaeger
2004-03-16 20:05 ` Andreas Jaeger [this message]
2004-03-16 20:12 ` Ulrich Drepper
2004-03-17 5:33 ` Andreas Jaeger
2004-03-17 5:50 ` Ulrich Drepper
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