Re: [Qemu-devel] [PATCH v2] pc: Don't make die-id mandatory unless necessary

[Igor Mammedov]

On Fri, 16 Aug 2019 14:07:50 -0300
Eduardo Habkost <address@hidden> wrote:

> We have this issue reported when using libvirt to hotplug CPUs:
> https://bugzilla.redhat.com/show_bug.cgi?id=1741451
> 
> Basically, libvirt is not copying die-id from
> query-hotpluggable-cpus, but die-id is now mandatory.
> 
> We could blame libvirt and say it is not following the documented
> interface, because we have this buried in the QAPI schema
> documentation:
> 
> > Note: currently there are 5 properties that could be present
> > but management should be prepared to pass through other
> > properties with device_add command to allow for future
> > interface extension. This also requires the filed names to be kept in
> > sync with the properties passed to -device/device_add.  
> 
> But I don't think this would be reasonable from us.  We can just
> make QEMU more flexible and let die-id to be omitted when there's
> no ambiguity.  This will allow us to keep compatibility with
> existing libvirt versions.
> 
> Test case included to ensure we don't break this again.
> 
> Fixes: commit 176d2cda0dee ("i386/cpu: Consolidate die-id validity in smp 
> context")
> Signed-off-by: Eduardo Habkost <address@hidden>

Reviewed-by: Igor Mammedov <address@hidden>

> ---
> Changes v1 -> v2:
> * v1 was "pc: Don't make CPU properties mandatory unless necessary"
> * Make only die-id optional (Igor Mammedov)
> ---
>  hw/i386/pc.c                             |  8 ++++++
>  tests/acceptance/pc_cpu_hotplug_props.py | 35 ++++++++++++++++++++++++
>  2 files changed, 43 insertions(+)
>  create mode 100644 tests/acceptance/pc_cpu_hotplug_props.py
> 
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index 3ab4bcb3ca..9c3f6ae828 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -2406,6 +2406,14 @@ static void pc_cpu_pre_plug(HotplugHandler 
> *hotplug_dev,
>          int max_socket = (ms->smp.max_cpus - 1) /
>                                  smp_threads / smp_cores / pcms->smp_dies;
>  
> +        /*
> +         * die-id was optional in QEMU 4.0 and older, so keep it optional
> +         * if there's only one die per socket.
> +         */
> +        if (cpu->die_id < 0 && pcms->smp_dies == 1) {
> +            cpu->die_id = 0;
> +        }
> +
>          if (cpu->socket_id < 0) {
>              error_setg(errp, "CPU socket-id is not set");
>              return;
> diff --git a/tests/acceptance/pc_cpu_hotplug_props.py 
> b/tests/acceptance/pc_cpu_hotplug_props.py
> new file mode 100644
> index 0000000000..08b7e632c6
> --- /dev/null
> +++ b/tests/acceptance/pc_cpu_hotplug_props.py
> @@ -0,0 +1,35 @@
> +#
> +# Ensure CPU die-id can be omitted on -device
> +#
> +#  Copyright (c) 2019 Red Hat Inc
> +#
> +# Author:
> +#  Eduardo Habkost <address@hidden>
> +#
> +# This library is free software; you can redistribute it and/or
> +# modify it under the terms of the GNU Lesser General Public
> +# License as published by the Free Software Foundation; either
> +# version 2 of the License, or (at your option) any later version.
> +#
> +# This library is distributed in the hope that it will be useful,
> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +# Lesser General Public License for more details.
> +#
> +# You should have received a copy of the GNU Lesser General Public
> +# License along with this library; if not, see 
> <http://www.gnu.org/licenses/>.
> +#
> +
> +from avocado_qemu import Test
> +
> +class OmittedCPUProps(Test):
> +    """
> +    :avocado: tags=arch:x86_64
> +    """
> +    def test_no_die_id(self):
> +        self.vm.add_args('-nodefaults', '-S')
> +        self.vm.add_args('-smp', '1,sockets=2,cores=2,threads=2,maxcpus=8')
> +        self.vm.add_args('-cpu', 'qemu64')
> +        self.vm.add_args('-device', 
> 'qemu64-x86_64-cpu,socket-id=1,core-id=0,thread-id=0')
> +        self.vm.launch()
> +        self.assertEquals(len(self.vm.command('query-cpus')), 2)