Re: [Qemu-devel] [PATCH 0/3] vhost-user reconnect

[Yury Kotov]

16.08.2018, 18:36, "Marc-André Lureau" <address@hidden>:
> On Thu, Aug 16, 2018 at 5:32 PM, Yury Kotov <address@hidden> wrote:
>>  We are using QEMU (2.12.0) with SPDK (18.04.1) over vhost-user to emulate 
>> block
>>  devices. One of our cases it to restart SPDK without restarting VM (in case
>>  of some updates or smth like it). We tried to use the 'reconnect' option for
>>  the '-chardev' device:
>>    -object 
>> memory-backend-file,id=mem0,size=1G,mem-path=/dev/hugepages,share=on \
>>    -numa node,memdev=mem0 \
>>    -chardev socket,id=spdk_vhost_blk1,path=/var/tmp/vhost.1,reconnect=10 \
>>    -device vhost-user-blk-pci,chardev=spdk_vhost_blk1,num-queues=4
>>
>>  After this, vhost-user-blk initialization fails with an error below:
>>    qemu-system-x86_64: -device ...: Failed to set msg fds.
>>    qemu-system-x86_64: -device ...: vhost-user-blk: vhost initialization 
>> failed:
>>                                     Operation not permitted
>>
>>  We got the same error with the latest QEMU (c542a9f9794ec8e0bc3f).
>>
>>  We made some investigations and found out that there are several issues:
>>
>>  1. Reconnect option postpones the first connection till machine init done 
>> event.
>>     But we need this connection during vhost blk device initialization which
>>     happens before the machine init done handling.
>>
>>  2. If the connection is forced, then the reconnection will be successful
>>     after SPDK restart. The problem is that virtual queue will not start.
>>     The reason for it is that virtual queue initialization commands
>>     should be resent:
>>     * VHOST_USER_SET_FEATURES
>>     * VHOST_USER_SET_MEM_TABLE
>>     * VHOST_USER_SET_VRING_NUM
>>     * VHOST_USER_SET_VRING_BASE
>>     * VHOST_USER_SET_VRING_ADDR
>>     * VHOST_USER_SET_VRING_KICK
>>     * VHOST_USER_SET_VRING_CALL
>>
>>  The patch set resolves both of these issues.
>>
>>  Test case:
>>
>>  1. Start fio process (inside VM):
>>       fio --name test --ioengine=libaio --iodepth=64 --bs=4096 \
>>           --rw=randrw --direct=1 --sync=1 --verify=md5 \
>>           --size=64M --filename=/dev/vda --loops=100
>>
>>  2. Restart SPDK many times.
>>     We are expecting that during SPDK restart fio will pause and fio should
>>     continue to work after restart completion.
>>
>>  3. fio process completed successfully without any error.
>
> Can you write a test case in vhost-user-test.c ? (perhaps under
> QTEST_VHOST_USER_FIXME scope...)
>

This is a great idea and we were definitely going to do that during coming 
couple of weeks. We thought that we could make a follow up commit with 
necessary tests added a bit later though, since currently we need to figure out 
the state of vhost-user tests in general, before we can try to add any new 
stuff, and that will take some time. So far we have stress-tested these fixes 
manually.

Do you suggest we wait with this series as well until we have all tests ready? 
Or do we proceed now and make a follow up series with vhost user tests later 
like we suggested?

>>  Yury Kotov (3):
>>    chardev: prevent extra connection attempt in tcp_chr_machine_done_hook
>>    vhost: refactor vhost_dev_start and vhost_virtqueue_start
>>    vhost-user: add reconnect support for vhost-user
>>
>>   chardev/char-socket.c | 5 +-
>>   hw/virtio/vhost-user.c | 65 ++++++++++++--
>>   hw/virtio/vhost.c | 223 +++++++++++++++++++++++++++++++---------------
>>   include/hw/virtio/vhost.h | 2 +
>>   4 files changed, 215 insertions(+), 80 deletions(-)
>>
>>  --
>>  2.7.4