Additional threads are required to service upcalls when we have CPU
isolation (in per-cpu dispatch mode). The formula used to calculate
the number of handler threads to create is as follows
handlers_n = min(next_prime(active_cores+1), total_cores)
Where next_prime is a function that returns the next numeric prime
number that is strictly greater than active_cores
Fixes: b1e517bd2f81 ("dpif-netlink: Introduce per-cpu upcall dispatch.")
Signed-off-by: Michael Santana <msant...@redhat.com>
---
lib/dpif-netlink.c | 32 ++++++++++++++++++++-
lib/ovs-thread.c | 69 ++++++++++++++++++++++++++++++++++++++++++++++
lib/ovs-thread.h | 3 ++
3 files changed, 103 insertions(+), 1 deletion(-)
diff --git a/lib/dpif-netlink.c b/lib/dpif-netlink.c
index 06e1e8ca0..53de16e12 100644
--- a/lib/dpif-netlink.c
+++ b/lib/dpif-netlink.c
@@ -2506,6 +2506,36 @@ dpif_netlink_handler_uninit(struct dpif_handler *handler)
}
#endif
+/*
+ * Calcuales and returns the number of handler threads needed based
+ * the following formula:
+ *
+ * handlers_n = min(next_prime(active_cores+1), total_cores)
+ *
+ * Where next_prime is a function that returns the next numeric prime
+ * number that is strictly greater than active_cores
+ */
+static uint32_t
+dpif_netlink_calculate_handlers_num(void)
+{
+ uint32_t next_prime_num;
+ uint32_t n_handlers = count_cpu_cores();
+ uint32_t total_cores = count_total_cores();
+
+ /*
+ * If we have isolated cores, add additional handler threads to
+ * service inactive cores in the unlikely event that traffic goes
+ * through inactive cores
+ */
+ if (n_handlers < total_cores) {
+ next_prime_num = next_prime(n_handlers +1, 10000000);
+ n_handlers = next_prime_num >= total_cores ?
+ total_cores : next_prime_num;
+ }
+
+ return n_handlers;
+}
+
static int
dpif_netlink_refresh_handlers_cpu_dispatch(struct dpif_netlink *dpif)
OVS_REQ_WRLOCK(dpif->upcall_lock)
@@ -2755,7 +2785,7 @@ dpif_netlink_number_handlers_required(struct dpif *dpif_,
uint32_t *n_handlers)
struct dpif_netlink *dpif = dpif_netlink_cast(dpif_);
if (dpif_netlink_upcall_per_cpu(dpif)) {
- *n_handlers = count_cpu_cores();
+ *n_handlers = dpif_netlink_calculate_handlers_num();
return true;
}
diff --git a/lib/ovs-thread.c b/lib/ovs-thread.c
index 805cba622..fc3080d7c 100644
--- a/lib/ovs-thread.c
+++ b/lib/ovs-thread.c
@@ -18,6 +18,7 @@
#include "ovs-thread.h"
#include <errno.h>
#include <poll.h>
+#include <math.h>
#ifndef _WIN32
#include <signal.h>
#endif
@@ -663,6 +664,74 @@ count_cpu_cores(void)
return n_cores > 0 ? n_cores : 0;
}
+/* Returns the total number of cores on the system, or 0 if the
+ * number cannot be determined. */
+int
+count_total_cores(void) {
+ long int n_cores;
+
+#ifndef _WIN32
+ n_cores = sysconf(_SC_NPROCESSORS_CONF);
+#else
+ n_cores = 0;
+ errno = ENOTSUP;
+#endif
+
+ return n_cores > 0 ? n_cores : 0;
+}
+
+/*
+ * Returns 1 if num is a prime number,
+ * Otherwise return 0
+ */
+uint32_t
+is_prime(uint32_t num)
+{
+ if ((num % 2) == 0) {
+ return num == 2;
+ }
+
+ uint32_t i;
+ uint32_t limit = sqrt((float) num);
+ for (i = 3; i <= limit; i += 2) {
+ if (num % i == 0) {
+ return 0;
+ }
+ }
+
+ return 1;
+}
+
+/*
+ * Returns num if num is a prime number. Otherwise returns the next
+ * prime greater than num. Search is limited by the limit variable.
+ *
+ * Returns 0 if num >= limit, or if no prime has been found between
+ * num and limit
+ */
+uint32_t
+next_prime(uint32_t num, uint32_t limit)
+{
+ if (num < 2) {
+ return 2;
+ }
+ if (num == 2) {
+ return 3;
+ }
+ if (num % 2 == 0) {
+ num++;
+ }
+
+ uint32_t i;
+ for (i = num; i < limit; i += 2) {
+ if (is_prime(i)) {
+ return i;
+ }
+ }
+
+ return 0;
+}
+
/* Returns 'true' if current thread is PMD thread. */
bool
thread_is_pmd(void)
diff --git a/lib/ovs-thread.h b/lib/ovs-thread.h
index 3b444ccdc..6c1ebd098 100644
--- a/lib/ovs-thread.h
+++ b/lib/ovs-thread.h
@@ -522,6 +522,9 @@ bool may_fork(void);
/* Useful functions related to threading. */
int count_cpu_cores(void);
+int count_total_cores(void);
+uint32_t is_prime(uint32_t num);
+uint32_t next_prime(uint32_t num, uint32_t limit);
bool thread_is_pmd(void);
#endif /* ovs-thread.h */
--
2.33.1
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