netdev - [PATCH net-next v1 3/4] virtio_net: enable premapped mode for merge and small by default

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Message-Id: <20241029084615.91049-4-xuanzhuo@linux.alibaba.com>
Date: Tue, 29 Oct 2024 16:46:14 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: netdev@...r.kernel.org
Cc: "Michael S. Tsirkin" <mst@...hat.com>,
	Jason Wang <jasowang@...hat.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	virtualization@...ts.linux.dev,
	Darren Kenny <darren.kenny@...cle.com>
Subject: [PATCH net-next v1 3/4] virtio_net: enable premapped mode for merge and small by default

Currently, the virtio core will perform a dma operation for each
buffer. Although, the same page may be operated multiple times.

In premapped mod, we can perform only one dma operation for the pages of
the alloc frag. This is beneficial for the iommu device.

kernel command line: intel_iommu=on iommu.passthrough=0

       |  strict=0  | strict=1
Before |  775496pps | 428614pps
After  | 1109316pps | 742853pps

In the 6.11, we disabled this feature because a regress [1].

Now, we fix the problem and re-enable it.

[1]: http://lore.kernel.org/all/8b20cc28-45a9-4643-8e87-ba164a540c0a@oracle.com

Tested-by: Darren Kenny <darren.kenny@...cle.com>
Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Acked-by: Jason Wang <jasowang@...hat.com>
---
 drivers/net/virtio_net.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 7557808e8c1f..ea433e9650eb 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -6107,6 +6107,17 @@ static int virtnet_alloc_queues(struct virtnet_info *vi)
 	return -ENOMEM;
 }
 
+static void virtnet_rq_set_premapped(struct virtnet_info *vi)
+{
+	int i;
+
+	for (i = 0; i < vi->max_queue_pairs; i++) {
+		/* error should never happen */
+		BUG_ON(virtqueue_set_dma_premapped(vi->rq[i].vq));
+		vi->rq[i].do_dma = true;
+	}
+}
+
 static int init_vqs(struct virtnet_info *vi)
 {
 	int ret;
@@ -6120,6 +6131,10 @@ static int init_vqs(struct virtnet_info *vi)
 	if (ret)
 		goto err_free;
 
+	/* disable for big mode */
+	if (!vi->big_packets || vi->mergeable_rx_bufs)
+		virtnet_rq_set_premapped(vi);
+
 	cpus_read_lock();
 	virtnet_set_affinity(vi);
 	cpus_read_unlock();
-- 
2.32.0.3.g01195cf9f