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

[Igor Mammedov <imammedo@redhat.com>]

On Mon, 27 May 2019 08:55:49 +0200
Laurent Vivier <lvivier@redhat.com> wrote:

> On 24/05/2019 22:14, Eduardo Habkost wrote:
> > 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
> > 
> >   
> 
> The idea is to provide the information to the user to help him to know 
> where the cpu can be plugged when it cannot on the node-id he originally 
> provided.
> 
> So all the solutions you propose sounds good to me.
> 
> I only need you and Igor agree on the same one.

We with Eduardo basically agree on contents/set of properties to print,
it is only different phrasing (Eduardo's suggestion is better than what we have now).
But lets get to what problem you are going to fix/improve. SO I've went ahead and tried
with following CLI:

   qemu-system-x86_64 -smp 1,maxcpus=4 -numa node,cpus=0-1 -numa node,cpus=2-3 -monitor stdio -device qemu64-x86_64-cpu,socket-id=1,core-id=0,thread-id=0,node-id=1

end it errored out with:

  qemu-system-x86_64: -device qemu64-x86_64-cpu,socket-id=1,core-id=0,thread-id=0,node-id=1: node-id=1 must match numa node specified with -numa option

As you see we already have all user provide properties for cpu (including invalid ones) reported,
what we are missing is suggestion for valid node-id. How about following error message:

qemu-system-x86_64: -device qemu64-x86_64-cpu,socket-id=1,core-id=0,thread-id=0,node-id=1: invalid node-id, must be 0

> 
> Thanks,
> Laurent