From c0f4d7a4edffb58f29a95262c4c248aa385d1863 Mon Sep 17 00:00:00 2001 From: Changchun Ouyang Date: Fri, 27 Mar 2015 13:20:06 +0000 Subject: [PATCH] doc: add common issues in vhost sample guide Added some documentation on common issues for the vhost sample app and how to resolve them. Signed-off-by: Changchun Ouyang Signed-off-by: John McNamara Acked-by: Siobhan Butler --- 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 d542929db0..cd9b232239 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. @@ -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 + + cat /sys/kernel/mm/hugepages/hugepages-/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-/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 ----------------------------------- -- 2.20.1