Re: [Qemu-devel] [RFC PATCH 2/2] numa: Add node_id data in query-hotpluggable-cpus

[Igor Mammedov]

On Fri, 8 Jul 2016 14:04:23 +0200
Peter Krempa <address@hidden> wrote:

> On Fri, Jul 08, 2016 at 13:54:58 +0200, Igor Mammedov wrote:
> > On Thu,  7 Jul 2016 17:17:14 +0200
> > Peter Krempa <address@hidden> wrote:
> >   
> > > Add a helper that looks up the NUMA node for a given CPU and use it to
> > > fill the node_id in the PPC and X86 impls of query-hotpluggable-cpus.
> > > 
> > > Signed-off-by: Peter Krempa <address@hidden>
> > > ---
> > >  hw/i386/pc.c          |  7 +++++++
> > >  hw/ppc/spapr.c        |  8 ++++++--
> > >  include/sysemu/numa.h |  1 +
> > >  numa.c                | 13 +++++++++++++
> > >  4 files changed, 27 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> > > index 4ba02c4..a0b9507 100644
> > > --- a/hw/i386/pc.c
> > > +++ b/hw/i386/pc.c
> > > @@ -2115,6 +2115,7 @@ static HotpluggableCPUList 
> > > *pc_query_hotpluggable_cpus(MachineState *machine)
> > >      HotpluggableCPUList *head = NULL;
> > >      PCMachineState *pcms = PC_MACHINE(machine);
> > >      const char *cpu_type;
> > > +    int node_id;
> > > 
> > >      cpu = pcms->possible_cpus->cpus[0].cpu;
> > >      assert(cpu); /* BSP is always present */
> > > @@ -2138,6 +2139,12 @@ static HotpluggableCPUList 
> > > *pc_query_hotpluggable_cpus(MachineState *machine)
> > >          cpu_props->core_id = topo.core_id;
> > >          cpu_props->has_thread_id = true;
> > >          cpu_props->thread_id = topo.smt_id;
> > > +
> > > +        if ((node_id = numa_node_get_by_cpu_index(i)) >= 0) {
> > > +            cpu_props->has_node_id = true;
> > > +            cpu_props->node_id = node_id;
> > > +        }  
> > I've not included node_id for a reason,
> >  "-numa cpus=1,2,3..." looks to me hopelessly broken now but
> > I've not came up with an idea how to redo it in nice and clean way yet.
> > 
> > Alternative could be CLI-less numa configuration, where QEMU is started
> > without "-numa cpus" but with "-S" then mgmt could call
> > query_hotpluggable_cpus() to get possible CPUs and then
> > map them to numa  nodes with a new QMP command using attributes
> > it got from query_hotpluggable_cpus().  
> 
> I think this could work for libvirt. The CPU index we currently expose
> in the XML would become just a libvirt internal detail and the new QMP
> command would be used to do the setup. Adding some QMP calls during VM
> startup is okay.
> 
> > it's along the way start QEMU -smp 1,maxcpus=X and then add
> > remaining CPUs with device_add after getting properties from
> > query_hotpluggable_cpus().  
> 
> I'm going to use a similar approach even for the hotpluggable cpus so I
> can query the data for a new VM. On the other hand I can't make libvirt
> use the approach with -smp 1,... all the time since we guarantee that a
> XML that worked on a older version will be migratable back to the older
> version.
Could you explain a little bit more about issue?

> 
> > then at machine_done time we can adjust DT/ACPI data to reflect
> > configured mapping.  
> 
> In such case this series can be dropped since it provides what I need
> differently.
> 
> Thanks,
> 
> Peter
>