netdev - [PATCH net-next v3 6/8] virtio-net: xsk zero copy xmit kick by threshold

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Date:   Wed, 31 Mar 2021 15:11:37 +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>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Björn Töpel <bjorn@...nel.org>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>,
        virtualization@...ts.linux-foundation.org, bpf@...r.kernel.org,
        Dust Li <dust.li@...ux.alibaba.com>
Subject: [PATCH net-next v3 6/8] virtio-net: xsk zero copy xmit kick by threshold

After testing, the performance of calling kick every time is not stable.
And if all the packets are sent and kicked again, the performance is not
good. So add a module parameter to specify how many packets are sent to
call a kick.

8 is a relatively stable value with the best performance.

Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Reviewed-by: Dust Li <dust.li@...ux.alibaba.com>
---
 drivers/net/virtio_net.c | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 259fafcf6028..d7e95f55478d 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -29,10 +29,12 @@ module_param(napi_weight, int, 0444);
 
 static bool csum = true, gso = true, napi_tx = true;
 static int xsk_budget = 32;
+static int xsk_kick_thr = 8;
 module_param(csum, bool, 0444);
 module_param(gso, bool, 0444);
 module_param(napi_tx, bool, 0644);
 module_param(xsk_budget, int, 0644);
+module_param(xsk_kick_thr, int, 0644);
 
 /* FIXME: MTU in config. */
 #define GOOD_PACKET_LEN (ETH_HLEN + VLAN_HLEN + ETH_DATA_LEN)
@@ -2612,6 +2614,8 @@ static int virtnet_xsk_xmit_batch(struct send_queue *sq,
 	struct xdp_desc desc;
 	int err, packet = 0;
 	int ret = -EAGAIN;
+	int need_kick = 0;
+	int kicks = 0;
 
 	if (sq->xsk.last_desc.addr) {
 		err = virtnet_xsk_xmit(sq, pool, &sq->xsk.last_desc);
@@ -2619,6 +2623,7 @@ static int virtnet_xsk_xmit_batch(struct send_queue *sq,
 			return -EBUSY;
 
 		++packet;
+		++need_kick;
 		--budget;
 		sq->xsk.last_desc.addr = 0;
 	}
@@ -2642,13 +2647,25 @@ static int virtnet_xsk_xmit_batch(struct send_queue *sq,
 		}
 
 		++packet;
+		++need_kick;
+		if (need_kick > xsk_kick_thr) {
+			if (virtqueue_kick_prepare(sq->vq) &&
+			    virtqueue_notify(sq->vq))
+				++kicks;
+
+			need_kick = 0;
+		}
 	}
 
 	if (packet) {
-		if (virtqueue_kick_prepare(sq->vq) &&
-		    virtqueue_notify(sq->vq)) {
+		if (need_kick) {
+			if (virtqueue_kick_prepare(sq->vq) &&
+			    virtqueue_notify(sq->vq))
+				++kicks;
+		}
+		if (kicks) {
 			u64_stats_update_begin(&sq->stats.syncp);
-			sq->stats.kicks += 1;
+			sq->stats.kicks += kicks;
 			u64_stats_update_end(&sq->stats.syncp);
 		}
 
-- 
2.31.0