Re: [dpdk-dev] [PATCH v4 3/3] vhost: fix offload flags in Rx path

["Wang, Yinan" <yinan.wang@intel.com>]

> -----Original Message-----
> From: David Marchand <david.marchand@redhat.com>
> Sent: 2021年5月12日 23:20
> To: Wang, Yinan <yinan.wang@intel.com>
> Cc: dev@dpdk.org; maxime.coquelin@redhat.com;
> olivier.matz@6wind.com; fbl@sysclose.org; i.maximets@ovn.org; Xia,
> Chenbo <chenbo.xia@intel.com>; Stokes, Ian <ian.stokes@intel.com>;
> stable@dpdk.org; Jijiang Liu <jijiang.liu@intel.com>; Yuanhan Liu
> <yuanhan.liu@linux.intel.com>
> Subject: Re: [dpdk-dev] [PATCH v4 3/3] vhost: fix offload flags in Rx path
> 
> On Wed, May 12, 2021 at 5:30 AM Wang, Yinan <yinan.wang@intel.com>
> wrote:
> >
> > Hi David,
> >
> > Since vhost tx offload can’t work now, we report a Bugzilla as below, could
> you help to take a look?
> > https://bugs.dpdk.org/show_bug.cgi?id=702
> 
> (I discovered your mail from 05/08 only today, now that I got a new
> mail, might be a pebcak from me, sorry...)
> 
> 
> - Looking at the bz, there is a first issue/misconception.
> testpmd only does TSO or any kind of tx offloading with the csum forward
> engine.
> The iofwd engine won't make TSO possible.
> 
> 
> - Let's say we use the csum fwd engine, testpmd configures drivers
> through the ethdev API.
> The ethdev API states that no offloading is enabled unless requested
> by the application.
> TSO, l3/l4 checksums offloading are documented as:
> https://doc.dpdk.org/guides/nics/features.html#l3-checksum-offload
> https://doc.dpdk.org/guides/nics/features.html#lro
> 
> But the vhost pmd does not report such capabilities.
> https://git.dpdk.org/dpdk/tree/drivers/net/vhost/rte_eth_vhost.c#n1276
> 
> So we can't expect testpmd to have tso working with net/vhost pmd.
> 
> 
> - The csum offloading engine swaps mac addresses.
> I would expect issues with inter vm traffic.
> 
> 
> In summary, I think this is a bad test.
> If it worked with the commands in the bugzilla before my change (which
> I doubt), it was wrong.

Thanks your kindly explanation. 
Before this patch, vhost can declare tso offload, if we configure TSO/csum in Qemu, tso offload flags can be marked, such vm2vm can fwd large pkts (64k when using iperf) with iofwd.
Now I am understand this case will not work later, we can move to using vswitch.

> 
> > We also tried vhost example with VM2VM iperf test, large pkts also can't
> forwarding.
> 
> "large pkts", can you give details?
> 
> I tried to use this example, without/with my change, but:
> 
> When I try to start this example with a physical port and two vhosts,
> I get a crash (division by 0 on vdmq stuff).
> When I start it without a physical port, I get a complaint about no
> port being enabled.
> Passing a portmask 0x1 seems to work, the example starts but, next, no
> traffic is forwarded (not even arp).
> Hooking gdb, I never get packet dequeued from vhost.

I re-test with vswitch, vm2vm iperf test can work w/ and w/o this patch. Sorry for the wrong result about vhost example before.
There are some special configuration in vswitch sample. Test steps can work as below:

1. Modify the testpmd code as following::
	--- a/examples/vhost/main.c
	+++ b/examples/vhost/main.c
	@@ -29,7 +29,7 @@
	 #include "main.h"

	 #ifndef MAX_QUEUES
	-#define MAX_QUEUES 128
	+#define MAX_QUEUES 512
	 #endif
	 /* the maximum number of external ports supported */

2. Bind one physical ports to vfio-pci, launch dpdk-vhost by below command::

	./dpdk-vhost -l 26-28 -n 4 -- -p 0x1 --mergeable 1 --vm2vm 1 --socket-file /tmp/vhost-net0 --socket-file /tmp/vhost-net1

3. Start VM0::

 	/home/qemu-install/qemu-4.2.1/bin/qemu-system-x86_64 -name vm1 -enable-kvm -cpu host -smp 4 -m 4096 \
        -object memory-backend-file,id=mem,size=4096M,mem-path=/mnt/huge,share=on \
        -numa node,memdev=mem -mem-prealloc -drive file=/home/osimg/ubuntu20-04.img  \
        -chardev socket,path=/tmp/vm2_qga0.sock,server,nowait,id=vm2_qga0 -device virtio-serial \
        -device virtserialport,chardev=vm2_qga0,name=org.qemu.guest_agent.2 -daemonize \
        -monitor unix:/tmp/vm2_monitor.sock,server,nowait -device e1000,netdev=nttsip1 \
        -netdev user,id=nttsip1,hostfwd=tcp:127.0.0.1:6002-:22 \
        -chardev socket,id=char0,path=/tmp/vhost-net0 \
        -netdev type=vhost-user,id=netdev0,chardev=char0,vhostforce \
        -device virtio-net-pci,netdev=netdev0,mac=52:54:00:00:00:01,disable-modern=true,mrg_rxbuf=off,csum=on,guest_csum=on,host_tso4=on,guest_tso4=on,guest_ecn=on -vnc :10

4. Start VM1::

	/home/qemu-install/qemu-4.2.1/bin/qemu-system-x86_64 -name vm2 -enable-kvm -cpu host -smp 4 -m 4096 \
        -object memory-backend-file,id=mem,size=4096M,mem-path=/mnt/huge,share=on \
        -numa node,memdev=mem -mem-prealloc -drive file=/home/osimg/ubuntu20-04-2.img  \
        -chardev socket,path=/tmp/vm2_qga0.sock,server,nowait,id=vm2_qga0 -device virtio-serial \
        -device virtserialport,chardev=vm2_qga0,name=org.qemu.guest_agent.2 -daemonize \
        -monitor unix:/tmp/vm2_monitor.sock,server,nowait -device e1000,netdev=nttsip1 \
        -netdev user,id=nttsip1,hostfwd=tcp:127.0.0.1:6003-:22 \
        -chardev socket,id=char0,path=/tmp/vhost-net1 \
        -netdev type=vhost-user,id=netdev0,chardev=char0,vhostforce \
        -device virtio-net-pci,netdev=netdev0,mac=52:54:00:00:00:02,disable-modern=true,mrg_rxbuf=off,csum=on,guest_csum=on,host_tso4=on,guest_tso4=on,guest_ecn=on -vnc :12
5. On VM1, set virtio device IP and run arp protocal::

    ifconfig ens5 1.1.1.2
    arp -s 1.1.1.8 52:54:00:00:00:02

6. On VM2, set virtio device IP and run arp protocal::

    ifconfig ens5 1.1.1.8
    arp -s 1.1.1.2 52:54:00:00:00:01

7. Check the iperf performance with different packet size between two VMs by below commands::

    Under VM1, run: `iperf -s -i 1`
    Under VM2, run: `iperf -c 1.1.1.2 -i 1 -t 60`

> 
> 
> --
> David Marchand