[dpdk-dev] [PATCH v4] doc: add driver limitation for vhost dequeue zero copy

[Maxime Coquelin]

On 03/29/2018 02:14 PM, Maxime Coquelin wrote:
> 
> 
> On 03/14/2018 05:24 PM, Junjie Chen wrote:
>> In vhost-switch example, when binding nic to vfio-pci with iommu enabled,
>> dequeue zero copy cannot work in VM2NIC mode due to no iommu dma mapping
>> is setup for guest memory currently.
>>
>> Signed-off-by: Junjie Chen <junjie.j.chen at intel.com>
> 
> Reviewed-by: Maxime Coquelin <maxime.coquelin at redhat.com>
> 
> John, as this is a doc patch for Vhost, does it go through the doc tree 
> or through Virtio one?


Applied to dpdk-next-virtio/master

Thanks,
Maxime

> Thanks,
> Maxime
>> ---
>> Changes in V4:
>> - make words more accurate
>> Changes in V3:
>> - update limitation to iommu
>> Changes in V2:
>> - add doc in vhost lib
>>   doc/guides/prog_guide/vhost_lib.rst | 5 +++++
>>   doc/guides/sample_app_ug/vhost.rst  | 5 ++++-
>>   2 files changed, 9 insertions(+), 1 deletion(-)
>>
>> diff --git a/doc/guides/prog_guide/vhost_lib.rst 
>> b/doc/guides/prog_guide/vhost_lib.rst
>> index 18227b6..b49e36e 100644
>> --- a/doc/guides/prog_guide/vhost_lib.rst
>> +++ b/doc/guides/prog_guide/vhost_lib.rst
>> @@ -83,6 +83,11 @@ The following is an overview of some key Vhost API 
>> functions:
>>         of those segments, thus the fewer the segments, the quicker we 
>> will get
>>         the mapping. NOTE: we may speed it by using tree searching in 
>> future.
>> +    * zero copy can not work when using vfio-pci with iommu mode 
>> currently, this
>> +      is because we don't setup iommu dma mapping for guest memory. 
>> If you have
>> +      to use vfio-pci driver, please insert vfio-pci kernel module in 
>> noiommu
>> +      mode.
>> +
>>     - ``RTE_VHOST_USER_IOMMU_SUPPORT``
>>       IOMMU support will be enabled when this flag is set. It is 
>> disabled by
>> diff --git a/doc/guides/sample_app_ug/vhost.rst 
>> b/doc/guides/sample_app_ug/vhost.rst
>> index a4bdc6a..f0bb169 100644
>> --- a/doc/guides/sample_app_ug/vhost.rst
>> +++ b/doc/guides/sample_app_ug/vhost.rst
>> @@ -147,7 +147,10 @@ retries on an RX burst, it takes effect only when 
>> rx retry is enabled. The
>>   default value is 15.
>>   **--dequeue-zero-copy**
>> -Dequeue zero copy will be enabled when this option is given.
>> +Dequeue zero copy will be enabled when this option is given. it is 
>> worth to
>> +note that if NIC is binded to driver with iommu enabled, dequeue zero 
>> copy
>> +cannot work at VM2NIC mode (vm2vm=0) due to currently we don't setup 
>> iommu
>> +dma mapping for guest memory.
>>   **--vlan-strip 0|1**
>>   VLAN strip option is removed, because different NICs have different 
>> behaviors
>>