Add some contents for vhost sample.
Signed-off-by: Changchun Ouyang <changchun.ouyang at intel.com>
---
Change in v2:
-- Refine its format to fit well with other parts.
doc/guides/sample_app_ug/vhost.rst | 52 +++++++++++++++++++++++++++++++++-----
1 file changed, 45 insertions(+), 7 deletions(-)
diff --git a/doc/guides/sample_app_ug/vhost.rst
b/doc/guides/sample_app_ug/vhost.rst
index fa53db6..76997da 100644
--- a/doc/guides/sample_app_ug/vhost.rst
+++ b/doc/guides/sample_app_ug/vhost.rst
@@ -640,19 +640,57 @@ To call the QEMU wrapper automatically from libvirt, the
following configuration
Common Issues
~~~~~~~~~~~~~
-**QEMU failing to allocate memory on hugetlbfs.**
+* QEMU failing to allocate memory on hugetlbfs:
-file_ram_alloc: can't mmap RAM pages: Cannot allocate memory
+ file_ram_alloc: can't mmap RAM pages: Cannot allocate memory
-When running QEMU the above error implies that it has failed to allocate
memory for the Virtual Machine on the hugetlbfs.
-This is typically due to insufficient hugepages being free to support the
allocation request.
-The number of free hugepages can be checked as follows:
+ When running QEMU the above error implies that it has failed to allocate
memory for the Virtual Machine on
+ the hugetlbfs. This is typically due to insufficient hugepages being free
to support the allocation request.
+ The number of free hugepages can be checked as follows:
-.. code-block:: console
+ .. code-block:: console
user at target:cat /sys/kernel/mm/hugepages/hugepages-<pagesize> /
nr_hugepages
-The command above indicates how many hugepages are free to support QEMU's
allocation request.
+ The command above indicates how many hugepages are free to support QEMU's
allocation request.
+
+* User space VHOST work properly with the guest with 2M sized hug pages:
+
+ The guest may have 2M or 1G sized huge pages file, the user space VHOST
can work properly in both cases.
+
+* User space VHOST will not work with QEMU without '-mem-prealloc' option:
+
+ The current implementation work properly only when the guest memory is
pre-allocated, so it is required to
+ use the correct QEMU version(e.g. 1.6) which supports '-mem-prealloc'; The
option '-mem-prealloc' must be
+ specified explicitly in QEMU command line.
+
+* User space VHOST will not work with QEMU version without shared memory
mapping:
+
+ As shared memory mapping is mandatory for user space VHOST to work
properly with the guest as user space VHOST
+ needs access the shared memory from the guest to receive and transmit
packets. It is important to make sure
+ the QEMU version used supports shared memory mapping.
+
+* Using libvirt "virsh create" the qemu-wrap.py spawns a new process to run
"qemu-kvm". This impacts the behavior
+ of the "virsh destroy" which kills the process running "qemu-wrap.py"
without actually destroying the VM (leaves
+ the "qemu-kvm" process running):
+
+ This following patch can fix this issue:
+ http://dpdk.org/ml/archives/dev/2014-June/003607.html
+
+* In Ubuntu environment, QEMU fail to start a new guest normally with user
space VHOST due to hug pages can't be
+ allocated for the new guest.*
+
+ The solution for this issue could be adding "-boot c" into QEMU command
line to make sure the huge pages are
+ allocated properly and then the guest will startup normally.
+
+ Use "cat /proc/meminfo" to check if there is any change in value of
HugePages_Total and HugePages_Free after the
+ guest startup.
+
+* Logging message: "eventfd_link: module verification failed: signature
and/or required key missing - tainting kernel"*
+
+ Ignore the above logging message. The message occurs due to the new module
eventfd_link, which is not a standard
+ module of Linux, but it is necessary for user space VHOST current
implementation(CUSE-based) to communicate with
+ the guest.
Running DPDK in the Virtual Machine
-----------------------------------
--
1.8.4.2
