linux-kernel - [PATCH 02/14] virtio_net: simplify virtnet_set

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Message-ID: <20241228184949.31582-3-yury.norov@gmail.com>
Date: Sat, 28 Dec 2024 10:49:34 -0800
From: Yury Norov <yury.norov@...il.com>
To: linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org,
	virtualization@...ts.linux.dev,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Jason Wang <jasowang@...hat.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>
Cc: Yury Norov <yury.norov@...il.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: [PATCH 02/14] virtio_net: simplify virtnet_set_affinity()

The inner loop may be replaced with the dedicated for_each_online_cpu_wrap.
It helps to avoid setting the same bits in the @mask more than once, in
case of group_size is greater than number of online CPUs.

Signed-off-by: Yury Norov <yury.norov@...il.com>
---
 drivers/net/virtio_net.c | 12 +++++++-----
 include/linux/cpumask.h  |  4 ++++
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 7646ddd9bef7..5e266486de1f 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -3826,7 +3826,7 @@ static void virtnet_set_affinity(struct virtnet_info *vi)
 	cpumask_var_t mask;
 	int stragglers;
 	int group_size;
-	int i, j, cpu;
+	int i, start = 0, cpu;
 	int num_cpu;
 	int stride;
 
@@ -3840,16 +3840,18 @@ static void virtnet_set_affinity(struct virtnet_info *vi)
 	stragglers = num_cpu >= vi->curr_queue_pairs ?
 			num_cpu % vi->curr_queue_pairs :
 			0;
-	cpu = cpumask_first(cpu_online_mask);
 
 	for (i = 0; i < vi->curr_queue_pairs; i++) {
 		group_size = stride + (i < stragglers ? 1 : 0);
 
-		for (j = 0; j < group_size; j++) {
+		for_each_online_cpu_wrap(cpu, start) {
+			if (!group_size--)
+				break;
 			cpumask_set_cpu(cpu, mask);
-			cpu = cpumask_next_wrap(cpu, cpu_online_mask,
-						nr_cpu_ids, false);
 		}
+
+		start = cpu < nr_cpu_ids ? cpu + 1 : start;
+
 		virtqueue_set_affinity(vi->rq[i].vq, mask);
 		virtqueue_set_affinity(vi->sq[i].vq, mask);
 		__netif_set_xps_queue(vi->dev, cpumask_bits(mask), i, XPS_CPUS);
diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 5cf69a110c1c..30042351f15f 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -1036,6 +1036,8 @@ extern const DECLARE_BITMAP(cpu_all_bits, NR_CPUS);
 
 #define for_each_possible_cpu_wrap(cpu, start)	\
 	for ((void)(start), (cpu) = 0; (cpu) < 1; (cpu)++)
+#define for_each_online_cpu_wrap(cpu, start)	\
+	for ((void)(start), (cpu) = 0; (cpu) < 1; (cpu)++)
 #else
 #define for_each_possible_cpu(cpu) for_each_cpu((cpu), cpu_possible_mask)
 #define for_each_online_cpu(cpu)   for_each_cpu((cpu), cpu_online_mask)
@@ -1044,6 +1046,8 @@ extern const DECLARE_BITMAP(cpu_all_bits, NR_CPUS);
 
 #define for_each_possible_cpu_wrap(cpu, start)	\
 	for_each_cpu_wrap((cpu), cpu_possible_mask, (start))
+#define for_each_online_cpu_wrap(cpu, start)	\
+	for_each_cpu_wrap((cpu), cpu_online_mask, (start))
 #endif
 
 /* Wrappers for arch boot code to manipulate normally-constant masks */
-- 
2.43.0