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

[Laurent Vivier]

On 28/05/2019 15:44, Eduardo Habkost wrote:
> On Mon, May 27, 2019 at 03:52:30PM +0200, Laurent Vivier wrote:
> > On 27/05/2019 14:50, Igor Mammedov wrote:
> > > On Mon, 27 May 2019 08:55:49 +0200
> > > Laurent Vivier <address@hidden> 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 <address@hidden> 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 <address@hidden>
> > > > > > > > ---
> > > > > > > >
> > > > > > > > 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
> >
> > The case I'm worrying about is when the cpu is hotplugged: we don't have the 
> > "-device ..." information.
> >
> >    $ qemu-system-ppc64 -nodefaults -nographic -monitor stdio -m 1G -smp 
> > 1,maxcpus=64,cores=1,threads=1,sockets=1 -numa node,nodeid=0 -numa node,nodeid=1
> >    QEMU 3.0.1 monitor - type 'help' for more information
> >    (qemu) device_add power8_v2.0-spapr-cpu-core,core-id=30,node-id=1
> >    node-id=1 must match numa node specified with -numa option
> >
> > So you can see the needed information is missing.
>
> What kind of essential information would be missing if we
> followed Igor's suggestion?
>
>     (qemu) device_add power8_v2.0-spapr-cpu-core,core-id=30,node-id=1
>     invalid node-id, must be 0

"invalid node-id, must be 0" is perfect for me. I update the patch.

Thank you,
Laurent