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

From: David Marchand <david.marchand@redhat.com>
To: "Wang, Yinan" <yinan.wang@intel.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>,
	"maxime.coquelin@redhat.com" <maxime.coquelin@redhat.com>,
	 "olivier.matz@6wind.com" <olivier.matz@6wind.com>,
	"fbl@sysclose.org" <fbl@sysclose.org>,
	 "i.maximets@ovn.org" <i.maximets@ovn.org>,
	"Xia, Chenbo" <chenbo.xia@intel.com>,
	"Stokes, Ian" <ian.stokes@intel.com>,
	"stable@dpdk.org" <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
Date: Wed, 12 May 2021 17:20:21 +0200	[thread overview]
Message-ID: <CAJFAV8zengeneG17vjHNA=Twtwp=zeZjF5=a_vUXtbv98PrwBQ@mail.gmail.com> (raw)
In-Reply-To: <BYAPR11MB2648F122110B5226E2994FAE8F529@BYAPR11MB2648.namprd11.prod.outlook.com>

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.

> 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.

-- 
David Marchand