From: Willy Tarreau <w@1wt.eu>
Date: Thu, 13 Mar 2025 09:27:22 +0000 (+0100)
Subject: MINOR: cpu-topo: rely on _SC_NPROCESSORS_CONF to trim maxcpus
X-Git-Tag: v3.2-dev8~89
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=041462c4af744b27e368243bdb2632ca4551ab22;p=thirdparty%2Fhaproxy.git

MINOR: cpu-topo: rely on _SC_NPROCESSORS_CONF to trim maxcpus

We don't want to constantly deal with as many CPUs as a cpuset can hold,
so let's first try to trim the value to what the system claims to support
via _SC_NPROCESSORS_CONF. It is obviously still subject to the limit of
the cpuset size though. The value is stored globally so that we can
reuse it elsewhere after initialization.
---

diff --git a/include/haproxy/cpu_topo.h b/include/haproxy/cpu_topo.h
index 139bc81ec..acc04268c 100644
--- a/include/haproxy/cpu_topo.h
+++ b/include/haproxy/cpu_topo.h
@@ -5,6 +5,8 @@
 #include <haproxy/cpuset.h>
 #include <haproxy/cpu_topo-t.h>
 
+extern int cpu_topo_maxcpus;
+extern int cpu_topo_lastcpu;
 extern struct ha_cpu_topo *ha_cpu_topo;
 
 #endif /* _HAPROXY_CPU_TOPO_H */
diff --git a/src/cpu_topo.c b/src/cpu_topo.c
index 7d60617ae..894d8197b 100644
--- a/src/cpu_topo.c
+++ b/src/cpu_topo.c
@@ -1,28 +1,50 @@
 #define _GNU_SOURCE
 
+#include <unistd.h>
 #include <haproxy/api.h>
 #include <haproxy/cpu_topo.h>
 
 /* CPU topology information, ha_cpuset_size() entries, allocated at boot */
+int cpu_topo_maxcpus  = -1;  // max number of CPUs supported by OS/haproxy
+int cpu_topo_lastcpu  = -1;  // last supposed online CPU (no need to look beyond)
 struct ha_cpu_topo *ha_cpu_topo = NULL;
 
+/* returns an optimal maxcpus for the current system. It will take into
+ * account what is reported by the OS, if any, otherwise will fall back
+ * to the cpuset size, which serves as an upper limit in any case.
+ */
+static int cpu_topo_get_maxcpus(void)
+{
+	int abs_max = ha_cpuset_size();
+
+#if defined(_SC_NPROCESSORS_CONF)
+	int n = (int)sysconf(_SC_NPROCESSORS_CONF);
+
+	if (n > 0 && n <= abs_max)
+		return n;
+#endif
+	return abs_max;
+}
+
 /* Allocates everything needed to store CPU topology at boot.
  * Returns non-zero on success, zero on failure.
  */
 static int cpu_topo_alloc(void)
 {
-	int maxcpus = ha_cpuset_size();
 	int cpu;
 
+	cpu_topo_maxcpus = cpu_topo_get_maxcpus();
+	cpu_topo_lastcpu = cpu_topo_maxcpus - 1;
+
 	/* allocate the structures used to store CPU topology info */
-	ha_cpu_topo = (struct ha_cpu_topo*)malloc(maxcpus * sizeof(*ha_cpu_topo));
+	ha_cpu_topo = (struct ha_cpu_topo*)malloc(cpu_topo_maxcpus * sizeof(*ha_cpu_topo));
 	if (!ha_cpu_topo)
 		return 0;
 
 	/* preset all fields to -1 except the index and the state flags which
 	 * are assumed to all be bound and online unless detected otherwise.
 	 */
-	for (cpu = 0; cpu < maxcpus; cpu++) {
+	for (cpu = 0; cpu < cpu_topo_maxcpus; cpu++) {
 		memset(&ha_cpu_topo[cpu], 0xff, sizeof(*ha_cpu_topo));
 		ha_cpu_topo[cpu].st  = 0;
 		ha_cpu_topo[cpu].idx = cpu;