Re: [dpdk-dev] [PATCH] examples/vhost: fix perf regression

["Xu, Qian Q" <qian.q.xu@intel.com>]

Tested-by: Qian Xu <qian.q.xu@intel.com>

- Test Commit: 8f6f24342281f59de0df7bd976a32f714d39b9a9
- OS/Kernel: Fedora 21/4.1.13
- GCC: gcc (GCC) 4.9.2 20141101 (Red Hat 4.9.2-1)
- CPU: Intel(R) Xeon(R) CPU E5-2695 v4 @ 2.10
- NIC: Intel(R) Ethernet Controller X710 for 10GbE SFP+
- Total 2 cases, 2 passed, 0 failed. 

Test Case1: Virtio-net IPV4 fwd performance with mergable=off

Summary: 
Launch the vhost-switch sample, and launch VM with 2 virtio-net devices, let 2 virtio-net run IPV4 fwd, send traffic to the NIC port and let the traffic go through 2 virtio-net devices. Check the performance.

Details: 
1. Bind one port to igb_uio. 
2. Run vhost switch sample with mergeable=0, disable mergeable. 
taskset -c 18-19 ./examples/vhost/build/vhost-switch -c 0xc0000 -n 4 --huge-dir /mnt/huge --socket-mem 1024,1024 -- -p 0x1 --mergeable 0 --vm2vm 0
3. Launch VM: 
taskset -c 22-23 \
/root/qemu-versions/qemu-2.6.0/x86_64-softmmu/qemu-system-x86_64 -name vm1 \
-cpu host -enable-kvm -m 2048 -object memory-backend-file,id=mem,size=2048M,mem-path=/mnt/huge,share=on -numa node,memdev=mem -mem-prealloc \
-smp cores=4 -drive file=/home/img/vm1.img  \
-chardev socket,id=char0,path=./vhost-net \
-netdev type=vhost-user,id=mynet1,chardev=char0,vhostforce \
-device virtio-net-pci,mac=52:54:00:00:00:01,netdev=mynet1,mrg_rxbuf=on \
-chardev socket,id=char1,path=./vhost-net \
-netdev type=vhost-user,id=mynet2,chardev=char1,vhostforce \
-device virtio-net-pci,mac=52:54:00:00:00:02,netdev=mynet2,mrg_rxbuf=on \
-netdev tap,id=ipvm1,ifname=tap3,script=/etc/qemu-ifup -device rtl8139,netdev=ipvm1,id=net0,mac=00:00:00:00:10:01 \
-vnc :3 -daemonize
4. Set IPV4 fwd rules in VM: 
virtio1=$1
virtio2=$2
systemctl stop firewalld.service
systemctl disable firewalld.service
systemctl stop ip6tables.service
systemctl disable ip6tables.service
systemctl stop iptables.service
systemctl disable iptables.service
systemctl stop NetworkManager.service
echo 1 >/proc/sys/net/ipv4/ip_forward
ip addr add 192.168.1.2/24 dev $virtio1
ip neigh add 192.168.1.1 lladdr 00:00:10:00:24:00 dev $virtio1
ip link set dev $virtio1 up

ip addr add 192.168.2.2/24 dev $virtio2
ip neigh add 192.168.2.1 lladdr 00:00:10:00:24:01 dev $virtio2
ip link set dev $virtio2 up

5. Send traffic to NIC and see the performance back from virtio2. The performance is back with the patch. 

Test Case2: Virtio-net IPV4 fwd performance with mergable=on
Similar steps, just one feature set is different, set mergable=1 in the vhost-switch sample, then the performance is good as before. 



Thanks
Qian

-----Original Message-----
From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Jianfeng Tan
Sent: Tuesday, July 19, 2016 9:53 PM
To: dev@dpdk.org
Cc: yuanhan.liu@linux.intel.com; Wang, Zhihong <zhihong.wang@intel.com>; Tan, Jianfeng <jianfeng.tan@intel.com>
Subject: [dpdk-dev] [PATCH] examples/vhost: fix perf regression

We find significant perfermance drop introduced by below commit, when vhost example is started with --mergeable 0 and inside vm, kernel virtio-net driver is used to do ip based forwarding.

The root cause is that below commit adds support for
VIRTIO_NET_F_GUEST_TSO4 and VIRTIO_NET_F_GUEST_TSO6, and when mergeable is disabled, it triggers big_packets path of virtio-net driver. In this path, virtio driver uses 19 desc with 18 4K-sized pages to receive each packet, so that it can receive a big packet with size of 64K. But QEMU only creates 256 desc entries for each vq, which results in that only 13 packets can be received. VM kernel can quickly handle those packets and go to sleep (HLT).

As QEMU has no option to set the desc entries of a vq, so here, we disable VIRTIO_NET_F_GUEST_TSO4 and VIRTIO_NET_F_GUEST_TSO6 with VIRTIO_NET_F_HOST_TSO4 and VIRTIO_NET_F_HOST_TSO6 when we disable tso of vhost example, to avoid VM kernel virtio driver go into big_packets path.

Fixes: 859b480d5afd ("vhost: add guest offload setting")

Reported-by: Qian Xu <qian.q.xu@intel.com>
Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
---
 examples/vhost/main.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/examples/vhost/main.c b/examples/vhost/main.c index 3b98f42..92a9823 100644
--- a/examples/vhost/main.c
+++ b/examples/vhost/main.c
@@ -327,6 +327,8 @@ port_init(uint8_t port)
 	if (enable_tso == 0) {
 		rte_vhost_feature_disable(1ULL << VIRTIO_NET_F_HOST_TSO4);
 		rte_vhost_feature_disable(1ULL << VIRTIO_NET_F_HOST_TSO6);
+		rte_vhost_feature_disable(1ULL << VIRTIO_NET_F_GUEST_TSO4);
+		rte_vhost_feature_disable(1ULL << VIRTIO_NET_F_GUEST_TSO6);
 	}
 
 	rx_rings = (uint16_t)dev_info.max_rx_queues;
--
2.7.4