[dpdk-dev] [PATCH v4] vhost: Add indirect descriptors support to the TX path

[Maxime Coquelin]

On 10/14/2016 09:24 AM, Wang, Zhihong wrote:
>
>
>> -----Original Message-----
>> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Maxime Coquelin
>> Sent: Tuesday, September 27, 2016 4:43 PM
>> To: yuanhan.liu at linux.intel.com; Xie, Huawei <huawei.xie at intel.com>;
>> dev at dpdk.org
>> Cc: vkaplans at redhat.com; mst at redhat.com;
>> stephen at networkplumber.org; Maxime Coquelin
>> <maxime.coquelin at redhat.com>
>> Subject: [dpdk-dev] [PATCH v4] vhost: Add indirect descriptors support to
>> the TX path
>>
>> Indirect descriptors are usually supported by virtio-net devices,
>> allowing to dispatch a larger number of requests.
>>
>> When the virtio device sends a packet using indirect descriptors,
>> only one slot is used in the ring, even for large packets.
>>
>> The main effect is to improve the 0% packet loss benchmark.
>> A PVP benchmark using Moongen (64 bytes) on the TE, and testpmd
>> (fwd io for host, macswap for VM) on DUT shows a +50% gain for
>> zero loss.
>>
>> On the downside, micro-benchmark using testpmd txonly in VM and
>> rxonly on host shows a loss between 1 and 4%.i But depending on
>> the needs, feature can be disabled at VM boot time by passing
>> indirect_desc=off argument to vhost-user device in Qemu.
>>
>> Signed-off-by: Maxime Coquelin <maxime.coquelin at redhat.com>
>
>
> Hi Maxime,
>
> Seems this patch can't with Windows virtio guest in my test.
> Have you done similar tests before?
>
> The way I test:
>
>  1. Make sure https://patchwork.codeaurora.org/patch/84339/ is applied
>
>  2. Start testpmd with iofwd between 2 vhost ports
>
>  3. Start 2 Windows guests connected to the 2 vhost ports
>
>  4. Disable firewall and assign IP to each guest using ipconfig
>
>  5. Use ping to test connectivity
>
> When I disable this patch by setting:
>
>     0ULL << VIRTIO_RING_F_INDIRECT_DESC,
>
> the connection is fine, but when I restore:
>
>     1ULL << VIRTIO_RING_F_INDIRECT_DESC,
>
> the connection is broken.

Just noticed I didn't reply to all this morning.
I sent a debug patch to Zhihong, which shows that indirect desc chaining
looks OK.

On my side, I just setup 2 Windows 2016 VMs, and confirm the issue.
I'll continue the investigation early next week.

Has anyone already tested Windows guest with vhost-net, which also has
indirect descs support?


Regards,
Maxime