[RFC PATCH 06/11] net: Function to check against maximum number for RPS queues

[Tom Herbert <tom@herbertland.com>]

Add rps_check_max_queues function which checks is the input number
is greater than rps_max_num_queues. If it is then set max_num_queues
to the value and recreating the sock_flow_table to update the
queue masks used in table entries.
---
 include/linux/netdevice.h  | 10 ++++++++
 net/core/sysctl_net_core.c | 48 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index d528aa61fea3..48ba1c1fc644 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -804,6 +804,16 @@ static inline void rps_record_sock_flow(struct rps_sock_flow_table *table,
 	}
 }
 
+int __rps_check_max_queues(unsigned int idx);
+
+static inline int rps_check_max_queues(unsigned int idx)
+{
+	if (idx < rps_max_num_queues)
+		return 0;
+
+	return __rps_check_max_queues(idx);
+}
+
 #ifdef CONFIG_RFS_ACCEL
 bool rps_may_expire_flow(struct net_device *dev, u16 rxq_index, u32 flow_id,
 			 u16 filter_id);
diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index d09471f29d89..743c46148135 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -127,6 +127,54 @@ static int rps_sock_flow_sysctl(struct ctl_table *table, int write,
 
 	return ret;
 }
+
+int __rps_check_max_queues(unsigned int idx)
+{
+	unsigned int old;
+	size_t size;
+	int ret = 0;
+
+	/* Assume maximum queues should be a least the number of CPUs.
+	 * This avoids too much thrashing of the sock flow table at
+	 * initialization.
+	 */
+	if (idx < nr_cpu_ids && nr_cpu_ids < RPS_MAX_QID)
+		idx = nr_cpu_ids;
+
+	if (idx > RPS_MAX_QID)
+		return -EINVAL;
+
+	mutex_lock(&sock_flow_mutex);
+
+	old = rps_max_num_queues;
+	rps_max_num_queues = idx;
+
+	/* No need to reallocate table since nothing is changing */
+
+	if (roundup_pow_of_two(old) != roundup_pow_of_two(idx)) {
+		struct rps_sock_flow_table *sock_table;
+
+		sock_table = rcu_dereference_protected(rps_sock_flow_table,
+						       lockdep_is_held(&sock_flow_mutex));
+		size = sock_table ? sock_table->mask + 1 : 0;
+
+		/* Force creation of a new rps_sock_flow_table. It's
+		 * the same size as the existing table, but we expunge
+		 * any stale queue entries that would refer to the old
+		 * queue mask.
+		 */
+		ret = rps_create_sock_flow_table(size, size,
+						 sock_table, true);
+		if (ret)
+			rps_max_num_queues = old;
+	}
+
+	mutex_unlock(&sock_flow_mutex);
+
+	return ret;
+}
+EXPORT_SYMBOL(__rps_check_max_queues);
+
 #endif /* CONFIG_RPS */
 
 #ifdef CONFIG_NET_FLOW_LIMIT
-- 
2.25.1