[dpdk-dev,v4] doc: Update doc for vhost sample

From: Ouyang Changchun <changchun.ouyang@intel.com>

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>
---
 doc/guides/sample_app_ug/vhost.rst | 58 ++++++++++++++++++++++++++++++++------
 1 file changed, 50 insertions(+), 8 deletions(-)
  

> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of John McNamara
> Sent: Friday, March 27, 2015 1:20 PM
> To: dev@dpdk.org
> Subject: [dpdk-dev] [PATCH v4] doc: Update doc for vhost sample
> 
> From: Ouyang Changchun <changchun.ouyang@intel.com>
> 
> 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>
> ---
>  doc/guides/sample_app_ug/vhost.rst | 58
> ++++++++++++++++++++++++++++++++------
>  1 file changed, 50 insertions(+), 8 deletions(-)
> 
> diff --git a/doc/guides/sample_app_ug/vhost.rst
> b/doc/guides/sample_app_ug/vhost.rst
> index 4a6d434..7e333cf 100644
> --- a/doc/guides/sample_app_ug/vhost.rst
> +++ b/doc/guides/sample_app_ug/vhost.rst
> @@ -1,3 +1,4 @@
> +
>  ..  BSD LICENSE
>      Copyright(c) 2010-2014 Intel Corporation. All rights reserved.
>      All rights reserved.
> @@ -640,19 +641,60 @@ 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
> +
> +        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``:
> 
> -    user@target:cat /sys/kernel/mm/hugepages/hugepages-<pagesize> /
> nr_hugepages
> +    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
>  -----------------------------------
> --
> V4: Fixed typos and syntax.
> V3: Fixed indentation issue that prevented PDFs from building.
> 
> 
> 1.8.1.4

Acked-by Siobhan Butler <siobhan.a.butler@intel.com>
  

> > From: Ouyang Changchun <changchun.ouyang@intel.com>
> > 
> > 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>

Applied, thanks