Re: [Qemu-devel] [PATCH 3/4] acpi: provide _PXM method for CPU devices if QEMU is started numa enabled

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Jun 30, 2016 at 04:11:44PM +0300, Marcel Apfelbaum wrote:
> On 06/30/2016 04:01 PM, Igor Mammedov wrote:
> > On Thu, 30 Jun 2016 15:48:54 +0300
> > Marcel Apfelbaum <marcel@redhat.com> wrote:
> > 
> > > On 06/30/2016 03:23 PM, Igor Mammedov wrote:
> > > > fixes long standing issue where Linux kernel would assing
> > > > hotplugged CPU to 1st numa node as it discards proximity
> > > > for hotplugged CPUs after SRAT is parsed.
> > > > 
> > > > Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> > > > ---
> > > >    hw/acpi/cpu.c | 9 +++++++++
> > > >    1 file changed, 9 insertions(+)
> > > > 
> > > > diff --git a/hw/acpi/cpu.c b/hw/acpi/cpu.c
> > > > index c13b65c..d9cf3ee 100644
> > > > --- a/hw/acpi/cpu.c
> > > > +++ b/hw/acpi/cpu.c
> > > > @@ -4,6 +4,7 @@
> > > >    #include "qapi/error.h"
> > > >    #include "qapi-event.h"
> > > >    #include "trace.h"
> > > > +#include "sysemu/numa.h"
> > > > 
> > > >    #define ACPI_CPU_HOTPLUG_REG_LEN 12
> > > >    #define ACPI_CPU_SELECTOR_OFFSET_WR 0
> > > > @@ -503,6 +504,7 @@ void build_cpus_aml(Aml *table, MachineState *machine, CPUHotplugFeatures opts,
> > > > 
> > > >            /* build Processor object for each processor */
> > > >            for (i = 0; i < arch_ids->len; i++) {
> > > > +            int j;
> > > >                Aml *dev;
> > > >                Aml *uid = aml_int(i);
> > > >                GArray *madt_buf = g_array_new(0, 1, 1);
> > > > @@ -546,6 +548,13 @@ void build_cpus_aml(Aml *table, MachineState *machine, CPUHotplugFeatures opts,
> > > >                              aml_arg(1), aml_arg(2))
> > > >                );
> > > >                aml_append(dev, method);
> > > > +
> > > > +            for (j = 0; j < nb_numa_nodes; j++) {
> > > > +                if (test_bit(i, numa_info[j].node_cpu)) {
> > > > +                    aml_append(dev, aml_name_decl("_PXM", aml_int(j)));
> > > > +                }
> > > > +            }
> > > > +
> > > >                aml_append(cpus_dev, dev);
> > > >            }
> > > >        }
> > > > 
> > > 
> > > I would add, at least in the commit message, a pointer to the ACPI spec:
> > > 
> > > ACPI 5.0 (6.2.13)
> > > -----------------
> > > If the Local APIC ID / Local SAPIC ID / Local x2APIC ID of a dynamically added processor is not
> > > present in the System Resource Affinity Table (SRAT), a _PXM object must exist for the
> > > processor’s device or one of its ancestors in the ACPI Namespace.
> > > 
> > > 
> > > I suppose we don't have the APIC id in SRAT for all possible CPUs, so it OK.
> > we have entries for possible CPUs in SRAT and commit says that Linux discards it,
> > hence we need to add _PXM to CPU objects. So broken linux handling would put
> > hotplugged CPUs into corrected nodes.
> > 
> 
> OK, so the commit message was misleading: "Fixes" :)
> Just flip "Fix" with "Workaround for... "
> 
> > To fix it on linux side, ACPI part probably would need to be refactored to store
> > parsed tables info somewhere else, so it would be available past boot time
> > (not a small undertaking) I'd say.
> 
> Maybe we should at least report it to the right mailing list.

For sure, this can't hurt, but does not have to block
this patch.

> 
> > While fixing it on QEMU side is easy and works well even for currently released
> > kernels.
> > 
> 
> I have nothing against this approach.
> 
> Thanks,
> Marcel
> 
> > 
> > > 
> > > 
> > > Reviewed-by: Marcel Apfelbaum <marcel@redhat.com>
> > Thanks!
> > 
> > > 
> > > Thanks,
> > > Marcel
> >