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authorAdhemerval Zanella <adhemerval.zanella@linaro.org>2021-03-24 18:56:34 -0300
committerAdhemerval Zanella <adhemerval.zanella@linaro.org>2021-05-07 13:35:29 -0300
commitdb373e4c57159ac82df4b07b596dd29c4cfe9d86 (patch)
treeaf01c60f6c1bbb8e2881fb7fc43bca85330d853c /posix
parent69e0a5eb0d5acb4b55dbef68b68fc4a10f2911af (diff)
downloadglibc-db373e4c57159ac82df4b07b596dd29c4cfe9d86.tar.gz
Remove architecture specific sched_cpucount optimizations
And replace the generic algorithm with the Brian Kernighan's one. GCC optimize it with popcnt if the architecture supports, so there is no need to add the extra POPCNT define to enable it. This is really a micro-optimization that only adds complexity: recent ABIs already support it (x86-64-v2 or power64le) and it simplifies the code for internal usage, since i686 does not allow an internal iFUNC call. Checked on x86_64-linux-gnu, aarch64-linux-gnu, and powerpc64le-linux-gnu.
Diffstat (limited to 'posix')
-rw-r--r--posix/sched_cpucount.c40
1 files changed, 14 insertions, 26 deletions
diff --git a/posix/sched_cpucount.c b/posix/sched_cpucount.c
index b0ca4ea7bc..63d0e99590 100644
--- a/posix/sched_cpucount.c
+++ b/posix/sched_cpucount.c
@@ -17,36 +17,24 @@
#include <sched.h>
+/* Counting bits set, Brian Kernighan's way.
+ Using a open-coded routine is slight better for architectures that
+ do not have a popcount instruction (compiler might emit a library
+ call). */
+static inline int
+countbits (__cpu_mask v)
+{
+ int s = 0;
+ for (; v != 0; s++)
+ v &= v - 1;
+ return s;
+}
int
__sched_cpucount (size_t setsize, const cpu_set_t *setp)
{
int s = 0;
- const __cpu_mask *p = setp->__bits;
- const __cpu_mask *end = &setp->__bits[setsize / sizeof (__cpu_mask)];
-
- while (p < end)
- {
- __cpu_mask l = *p++;
-
-#ifdef POPCNT
- s += POPCNT (l);
-#else
- if (l == 0)
- continue;
-
- _Static_assert (sizeof (l) == sizeof (unsigned int)
- || sizeof (l) == sizeof (unsigned long)
- || sizeof (l) == sizeof (unsigned long long),
- "sizeof (__cpu_mask");
- if (sizeof (__cpu_mask) == sizeof (unsigned int))
- s += __builtin_popcount (l);
- else if (sizeof (__cpu_mask) == sizeof (unsigned long))
- s += __builtin_popcountl (l);
- else
- s += __builtin_popcountll (l);
-#endif
- }
-
+ for (int i = 0; i < setsize / sizeof (__cpu_mask); i++)
+ s += countbits (setp->__bits[i]);
return s;
}