Re: [Qemu-arm] [Qemu-devel] [PATCH v3] numa: improve cpu hotplug error message with a wrong node-id

[Eduardo Habkost <ehabkost@redhat.com>]

On Fri, May 24, 2019 at 04:39:12PM +0200, Laurent Vivier wrote:
> On 24/05/2019 16:10, Igor Mammedov wrote:
> > On Fri, 24 May 2019 12:35:21 +0200
> > Laurent Vivier <lvivier@redhat.com> wrote:
> > 
> > > On pseries, core-ids are strongly binded to a node-id by the command
> > > line option. If an user tries to add a CPU to the wrong node, he has
> > > an error but it is not really helpful:
> > > 
> > >    qemu-system-ppc64 ... -smp 1,maxcpus=64,cores=1,threads=1,sockets=1 \
> > >                          -numa node,nodeid=0 -numa node,nodeid=1 ...
> > > 
> > >    (qemu) device_add power9_v2.0-spapr-cpu-core,core-id=30,node-id=1
> > >    Error: node-id=1 must match numa node specified with -numa option
> > > 
> > > This patch improves this error message by giving to the user the good
> > > topology information (node-id, socket-id and thread-id if they are
> > > available) to use with the core-id he's providing:
> > > 
> > >    Error: node-id=1 must match numa node specified with -numa option 'node-id 0'
> > > 
> > > Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> > > ---
> > > 
> > > Notes:
> > >      v3: only add the topology to the existing message
> > >          As suggested by Igor replace
> > >            Error: core-id 30 can only be plugged into node-id 0
> > >          by
> > >            Error: node-id=1 must match numa node specified with -numa option 'node-id 0'
> > >      v2: display full topology in the error message
> > > > > >   numa.c | 25 ++++++++++++++++++++++++-
> > >   1 file changed, 24 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/numa.c b/numa.c
> > > index 3875e1efda3a..7882ec294be4 100644
> > > --- a/numa.c
> > > +++ b/numa.c
> > > @@ -458,6 +458,27 @@ void qmp_set_numa_node(NumaOptions *cmd, Error **errp)
> > >       set_numa_options(MACHINE(qdev_get_machine()), cmd, errp);
> > >   }
> > > +static char *cpu_topology_to_string(const CPUArchId *cpu)
> > > +{
> > > +    GString *s = g_string_new(NULL);
> > > +    if (cpu->props.has_socket_id) {
> > > +        g_string_append_printf(s, "socket-id %"PRId64, cpu->props.socket_id);
> > > +    }
> > > +    if (cpu->props.has_node_id) {
> > > +        if (s->len) {
> > > +            g_string_append_printf(s, ", ");
> > > +        }
> > > +        g_string_append_printf(s, "node-id %"PRId64, cpu->props.node_id);
> > > +    }
> > > +    if (cpu->props.has_thread_id) {
> > > +        if (s->len) {
> > > +            g_string_append_printf(s, ", ");
> > > +        }
> > > +        g_string_append_printf(s, "thread-id %"PRId64, cpu->props.thread_id);
> > > +    }
> > > +    return g_string_free(s, false);
> > > +}
> > 
> > turns out we already have such helper: cpu_slot_to_string()
> 
> It doesn't display the node-id but the core-id. And node-id is what we need
> to know.

I'm confused about what you are trying to do here.

On v1, the message looked like:
  Error: core-id 30 can only be plugged into node-id 0

which is probably good for spapr.


Then I suggested you added the other cpu->props fields.  e.g. on
PC the message would look like:
  Error: socket-id 20, core-id 30, thread-id 40 can only be plugged into node-id 0


But you sent a v2 patch that would print this on PC:
  Error: core-id 30 can only be plugged into socket-id 20, node-id 0, thread-id 40

which doesn't make sense to me.


Then in a reply to v2, Igor suggested:

 error_setg(errp, "node-id=%d must match numa node specified "
                   "with -numa option '%s'", node_id, topology);


Igor suggest would address the problem above.  I expected it to become:
  node-id=0 must match numa node specified with -numa option core-id=30
and on PC:
  node-id=0 must match numa node specified with -numa option socket-id=20,core-id=30,thread-id=40

Or maybe it could include the input node-id too:
  node-id=0 must match numa node specified with -numa option node-id=1,core-id=30
and on PC:
  node-id=0 must match numa node specified with -numa option node-id=1,socket-id=20,core-id=30,thread-id=40

Both options would work.


But you implemented code that would print:
  Error: node-id=0 must match numa node specified with -numa option 'node-id 1'
and on PC it would print:
  Error: node-id=0 must match numa node specified with -numa option 'socket-id 20 node-id 1 thread-id=40'

which doesn't make sense to me.


I was expecting something like:
  Error: CPU slot core-id=30 is bound to node-id 0, but node-id 1 was specified
and on PC:
  Error: CPU slot socket-id=20,core-id=30,thread-id=40 is bound to node-id 0, but node-id 1 was specified


-- 
Eduardo