Re: libgo patch committed: Support NumCPU on more platforms

[Ian Lance Taylor]

On Tue, Aug 7, 2012 at 5:21 AM, Richard Earnshaw <rearn...@arm.com> wrote:
>
> Wouldn't it be more useful on Linux to check the task's affinity
> settings?  Then when a task is locked to a limited set of cores it won't
> overload those cores with threads.

This suggestion was implemented by Shenghou Ma, as attached.
Bootstrapped and ran Go testsuite on x86_64-unknown-linux-gnu.
Committed to mainline.

Ian

diff -r 8fc45a01251d libgo/runtime/getncpu-linux.c
--- a/libgo/runtime/getncpu-linux.c     Mon Aug 06 21:42:17 2012 -0700
+++ b/libgo/runtime/getncpu-linux.c     Thu Aug 09 23:04:31 2012 -0700
@@ -2,46 +2,35 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-#include <string.h>
-#include <sys/types.h>
-#include <fcntl.h>
-#include <unistd.h>
+#include <features.h>
+#include <sched.h>
+
+// CPU_COUNT is only provided by glibc 2.6 or higher
+#if !defined(__GLIBC_PREREQ) || !__GLIBC_PREREQ(2, 6)
+#define CPU_COUNT(set) _CPU_COUNT((unsigned int *)(set), 
sizeof(*(set))/sizeof(unsigned int))
+static int _CPU_COUNT(unsigned int *set, size_t len) {
+       int cnt;
+
+       cnt = 0;
+       while (len--)
+               cnt += __builtin_popcount(*set++);
+       return cnt;
+}
+#endif
 
 #include "runtime.h"
 #include "defs.h"
 
-#ifndef O_CLOEXEC
-#define O_CLOEXEC 0
-#endif
-
 int32
 getproccount(void)
 {
-       int32 fd, rd, cnt, cpustrlen;
-       const char *cpustr;
-       const byte *pos;
-       byte *bufpos;
-       byte buf[256];
+       cpu_set_t set;
+       int32 r, cnt;
 
-       fd = open("/proc/stat", O_RDONLY|O_CLOEXEC, 0);
-       if(fd == -1)
-               return 1;
        cnt = 0;
-       bufpos = buf;
-       cpustr = "\ncpu";
-       cpustrlen = strlen(cpustr);
-       for(;;) {
-               rd = read(fd, bufpos, sizeof(buf)-cpustrlen);
-               if(rd == -1)
-                       break;
-               bufpos[rd] = 0;
-               for(pos=buf; (pos=(const byte*)strstr((const char*)pos, 
cpustr)) != nil; cnt++, pos++) {
-               }
-               if(rd < cpustrlen)
-                       break;
-               memmove(buf, bufpos+rd-cpustrlen+1, cpustrlen-1);
-               bufpos = buf+cpustrlen-1;
-       }
-       close(fd);
+       r = sched_getaffinity(0, sizeof(set), &set);
+       if(r == 0)
+               cnt += CPU_COUNT(&set);
+
        return cnt ? cnt : 1;
 }