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.c...@intel.com>
Reviewed-by: Maxime Coquelin <maxime.coque...@redhat.com>
John, as this is a doc patch for Vhost, does it go through the doc tree
or through Virtio one?
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
