Thanks for review and testing, Nick!

On Wed, Feb 05, 2025 at 05:00:23PM -0600, Nick Child wrote:

On Tue, Jan 28, 2025 at 11:46:31AM -0500, Yury Norov wrote:

quoted

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.

nit: Looking at the previous logic of how group_stride is calculated, I don't
think there is possibility of "setting the same bits in the @mask more
than once". group_stride = n_cpu / n_queues

nit: I see this more as 2 patches. The introduction of a new core
helper function is a bit buried.

quoted

CC: Nick Child <nnac123@linux.ibm.com>
Signed-off-by: Yury Norov <yury.norov@gmail.com>

Don't know if my comments alone merit a v3 and I think the patch
does simplify the codebase so:
Reviewed-by: Nick Child <nnac123@linux.ibm.com>

I fixed the comments to #2 and #3 as you suggested and split-out new
for_each() loops to the new patch.

I also think those are trivial changes not worth v3. So it's in
bitmap-for-next:

https://github.com/norov/linux/tree/bitmap-for-next

Thanks for review, Nick!

Thanks,
Yury
 

quoted

---
 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..9d7c37e968b5 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--) {
+				start = cpu;
+				break;
+			}
 			cpumask_set_cpu(cpu, mask);
-			cpu = cpumask_next_wrap(cpu, cpu_online_mask,
-						nr_cpu_ids, false);
 		}
+
 		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