netdev - [PATCH v2] net: sort queues in xps maps

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Date:   Fri, 15 Jul 2022 10:31:58 +0800
From:   Yonglong Li <liyonglong@...natelecom.cn>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, alexanderduyck@...com,
        liyonglong@...natelecom.cn
Subject: [PATCH v2] net: sort queues in xps maps

in the following case that set xps of each tx-queue with same cpu mask,
packets in the same tcp stream may be hash to different tx queue. Because
the order of queues in each xps map is not the same.

first set each tx-queue with different cpu mask
$ echo 0 > /sys/class/net/eth0/queues/tx-0/xps_cpus
$ echo 1 > /sys/class/net/eth0/queues/tx-1/xps_cpus
$ echo 2 > /sys/class/net/eth0/queues/tx-2/xps_cpus
$ echo 4 > /sys/class/net/eth0/queues/tx-3/xps_cpus
and then set each tx-queue with same cpu mask
$ echo f > /sys/class/net/eth0/queues/tx-0/xps_cpus
$ echo f > /sys/class/net/eth0/queues/tx-1/xps_cpus
$ echo f > /sys/class/net/eth0/queues/tx-2/xps_cpus
$ echo f > /sys/class/net/eth0/queues/tx-3/xps_cpus

at this point the order of each map queues is differnet, It will cause
packets in the same stream be hashed to diffetent tx queue:
attr_map[0].queues = [0,1,2,3]
attr_map[1].queues = [1,0,2,3]
attr_map[2].queues = [2,0,1,3]
attr_map[3].queues = [3,0,1,2]

It is more reasonable that pacekts in the same stream be hashed to the same
tx queue when all tx queue bind with the same CPUs.

---
v1 -> v2:
Jakub suggestion: factor out the second loop in __netif_set_xps_queue() -
starting from the "add tx-queue to CPU/rx-queue maps" comment into a helper
---

Signed-off-by: Yonglong Li <liyonglong@...natelecom.cn>
---
 net/core/dev.c | 49 ++++++++++++++++++++++++++++++++-----------------
 1 file changed, 32 insertions(+), 17 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 978ed06..b9ae5d5 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -150,6 +150,7 @@
 #include <linux/pm_runtime.h>
 #include <linux/prandom.h>
 #include <linux/once_lite.h>
+#include <linux/sort.h>
 
 #include "dev.h"
 #include "net-sysfs.h"
@@ -199,6 +200,11 @@ static int call_netdevice_notifiers_extack(unsigned long val,
 
 static DECLARE_RWSEM(devnet_rename_sem);
 
+static int cmp_u16(const void *a, const void *b)
+{
+	return *(u16 *)a - *(u16 *)b;
+}
+
 static inline void dev_base_seq_inc(struct net *net)
 {
 	while (++net->dev_base_seq == 0)
@@ -2537,6 +2543,31 @@ static void xps_copy_dev_maps(struct xps_dev_maps *dev_maps,
 	}
 }
 
+static void update_xps_map(struct xps_map *map, int cpu, u16 index,
+			   bool *skip_tc, int *numa_node_id,
+			   enum xps_map_type type)
+{
+	int pos = 0;
+
+	*skip_tc = true;
+
+	while ((pos < map->len) && (map->queues[pos] != index))
+		pos++;
+
+	if (pos == map->len)
+		map->queues[map->len++] = index;
+
+	sort(map->queues, map->len, sizeof(u16), cmp_u16, NULL);
+#ifdef CONFIG_NUMA
+	if (type == XPS_CPUS) {
+		if (*numa_node_id == -2)
+			*numa_node_id = cpu_to_node(cpu);
+		else if (*numa_node_id != cpu_to_node(cpu))
+			*numa_node_id = -1;
+	}
+#endif
+}
+
 /* Must be called under cpus_read_lock */
 int __netif_set_xps_queue(struct net_device *dev, const unsigned long *mask,
 			  u16 index, enum xps_map_type type)
@@ -2629,24 +2660,8 @@ int __netif_set_xps_queue(struct net_device *dev, const unsigned long *mask,
 		if (netif_attr_test_mask(j, mask, nr_ids) &&
 		    netif_attr_test_online(j, online_mask, nr_ids)) {
 			/* add tx-queue to CPU/rx-queue maps */
-			int pos = 0;
-
-			skip_tc = true;
-
 			map = xmap_dereference(new_dev_maps->attr_map[tci]);
-			while ((pos < map->len) && (map->queues[pos] != index))
-				pos++;
-
-			if (pos == map->len)
-				map->queues[map->len++] = index;
-#ifdef CONFIG_NUMA
-			if (type == XPS_CPUS) {
-				if (numa_node_id == -2)
-					numa_node_id = cpu_to_node(j);
-				else if (numa_node_id != cpu_to_node(j))
-					numa_node_id = -1;
-			}
-#endif
+			update_xps_map(map, j, index, &skip_tc, &numa_node_id, type);
 		}
 
 		if (copy)
-- 
1.8.3.1