Re: [dpdk-dev] [PATCH v3] examples/vhost: fix perf regression

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

Add the tested-by:)

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

- Test Commit: 608487f3fc96704271c624d0f3fe9d7fb2187aea
- 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.

-----Original Message-----
From: Yuanhan Liu [mailto:yuanhan.liu@linux.intel.com] 
Sent: Thursday, July 21, 2016 9:34 AM
To: Tan, Jianfeng <jianfeng.tan@intel.com>
Cc: dev@dpdk.org; Wang, Zhihong <zhihong.wang@intel.com>; Xu, Qian Q <qian.q.xu@intel.com>
Subject: Re: [PATCH v3] examples/vhost: fix perf regression

On Thu, Jul 21, 2016 at 12:42:45AM +0000, Jianfeng Tan wrote:
> 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 commit, 859b480d5afd ("vhost: add guest offload setting"), adds 
> support for VIRTIO_NET_F_GUEST_TSO4 and VIRTIO_NET_F_GUEST_TSO6, in 
> vhost lib. But inside vhost example, the way to disable tso only 
> excludes the direction from virtio to vhost, but not the opposite 
> direction. When mergeable is disabled, it triggers big_packets path of 
> virtio-net driver to prepare to receive possible big packets with size 
> of 64K. Because mergeable is off, for each entry of avail ring, virtio 
> driver uses 19 desc chained together, with one desc pointing to 
> header, other 18 desc pointing to 4K-sized pages. 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: 9fd72e3cbd29 ("examples/vhost: add virtio offload")
> 
> Reported-by: Qian Xu <qian.q.xu@intel.com>
> Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
> ---
> v3: reword commit log.

Yes, much better. One minor nit: you forgot to carry the Tested-by from Qian.

Acked-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>

Thanks.

	--yliu