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doc: add common issues in vhost sample guide

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Added some documentation on common issues for the vhost sample app
and how to resolve them.

Signed-off-by: Changchun Ouyang <changchun.ouyang@intel.com>
Signed-off-by: John McNamara <john.mcnamara@intel.com>
Acked-by: Siobhan Butler <siobhan.a.butler@intel.com>
This commit is contained in:
Changchun Ouyang 2015-03-27 13:20:06 +00:00 committed by Thomas Monjalon
parent 9bc23cb820
commit c0f4d7a4ed
1 changed files with 50 additions and 8 deletions
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58
doc/guides/sample_app_ug/vhost.rst
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@ -1,3 +1,4 @@
.. BSD LICENSE
Copyright(c) 2010-2014 Intel Corporation. All rights reserved.
All rights reserved.
@ -713,19 +714,60 @@ 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, with an error like the following::
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 indicates 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@target:cat /sys/kernel/mm/hugepages/hugepages-<pagesize>/nr_hugepages
cat /sys/kernel/mm/hugepages/hugepages-<pagesize>/nr_hugepages
The command above indicates how many hugepages are free to support QEMU's allocation request.
* User space VHOST when the guest has 2MB sized huge pages:
The guest may have 2MB or 1GB sized huge pages. The user space VHOST should work properly in both cases.
* User space VHOST will not work with QEMU without the ``-mem-prealloc`` option:
The current implementation works properly only when the guest memory is pre-allocated, so it is required to
use a QEMU version (e.g. 1.6) which supports ``-mem-prealloc``. The ``-mem-prealloc`` option must be
specified explicitly in the QEMU command line.
* User space VHOST will not work with a QEMU version without shared memory mapping:
As shared memory mapping is mandatory for user space VHOST to work properly with the guest, user space VHOST
needs access to the shared memory from the guest to receive and transmit packets. It is important to make sure
the QEMU version supports shared memory mapping.
* Issues with ``virsh destroy`` not destroying the VM:
Using libvirt ``virsh create`` the ``qemu-wrap.py`` spawns a new process to run ``qemu-kvm``. This impacts the behavior
of ``virsh destroy`` which kills the process running ``qemu-wrap.py`` without actually destroying the VM (it leaves
the ``qemu-kvm`` process running):
This following patch should fix this issue:
http://dpdk.org/ml/archives/dev/2014-June/003607.html
* In an Ubuntu environment, QEMU fails to start a new guest normally with user space VHOST due to not being able
to allocate huge pages for the new guest:
The solution for this issue is to add ``-boot c`` into the QEMU command line to make sure the huge pages are
allocated properly and then the guest should start normally.
Use ``cat /proc/meminfo`` to check if there is any changes in the value of ``HugePages_Total`` and ``HugePages_Free``
after the guest startup.
* Log message: ``eventfd_link: module verification failed: signature and/or required key missing - tainting kernel``:
This log message may be ignored. The message occurs due to the kernel module ``eventfd_link``, which is not a standard
Linux module but which is necessary for the user space VHOST current implementation (CUSE-based) to communicate with
the guest.
The command above indicates how many hugepages are free to support QEMU's allocation request.
Running DPDK in the Virtual Machine
-----------------------------------