On Fri, 8 Jul 2016 17:59:07 +1000 David Gibson <da...@gibson.dropbear.id.au> wrote:
> On Fri, Jul 08, 2016 at 09:46:47AM +0200, Greg Kurz wrote:
> > On Fri, 8 Jul 2016 15:25:33 +1000
> > David Gibson <da...@gibson.dropbear.id.au> wrote:
> >
> > > On Thu, Jul 07, 2016 at 06:11:31PM +0200, Greg Kurz wrote:
> > > > On Thu, 7 Jul 2016 20:20:23 +0530
> > > > Bharata B Rao <bhar...@linux.vnet.ibm.com> wrote:
> > > >
> > > > > Conditonally set stable_cpu_id for CPU threads that are created as
> > > > > part
> > > > > of spapr CPU cores. The use of stable_cpu_id is enabled for
> > > > > pseries-2.7
> > > > > onwards.
> > > > >
> > > >
> > > > The last sentence is a bit confusing since the enablement actually
> > > > happens
> > > > in patch 5/5.
> > > >
> > > > > Signed-off-by: Bharata B Rao <bhar...@linux.vnet.ibm.com>
> > > > > ---
> > > > > hw/ppc/spapr_cpu_core.c | 7 +++++++
> > > > > 1 file changed, 7 insertions(+)
> > > > >
> > > > > diff --git a/hw/ppc/spapr_cpu_core.c b/hw/ppc/spapr_cpu_core.c
> > > > > index b104778..0ec3513 100644
> > > > > --- a/hw/ppc/spapr_cpu_core.c
> > > > > +++ b/hw/ppc/spapr_cpu_core.c
> > > > > @@ -293,8 +293,15 @@ static void spapr_cpu_core_realize(DeviceState
> > > > > *dev, Error **errp)
> > > > > for (i = 0; i < cc->nr_threads; i++) {
> > > > > char id[32];
> > > > > obj = sc->threads + i * size;
> > > > > + CPUState *cs;
> > > > >
> > > > > object_initialize(obj, size, typename);
> > > > > + cs = CPU(obj);
> > > > > +
> > > > > + /* Use core_id (which is actually cpu_dt_id) as stable CPU
> > > > > id */
> > > >
> > > > It isn't what I had in mind. More something like below:
> > > >
> > > > In ppc_spapr_init():
> > > >
> > > > for (i = 0; i < spapr_max_cores; i++) {
> > > > spapr->cores[i]->stable_id = i * smp_threads;
> > > > }
> > > >
> > > >
> > > > In spapr_cpu_core_realize():
> > > >
> > > > for (j = 0; j < cc->nr_threads; j++) {
> > > > stable_cpu_id = cc->stable_id + j;
> > > > }
> > > >
> > > > So we need to introduce cc->stable_id.
> > >
> > > No, we don't. Cores have had a stable ID since they were introduced.
> > >
> >
> > I agree core_dt_id is stable but it is a DT concept.
>
> There is no core_dt_id. There's just core-id, which is machine
> assigned (via the query hotpluggable cpus interface) and stable.
>
> > static void ppc_spapr_init(MachineState *machine)
> > {
> > [...]
> > for (i = 0; i < spapr_max_cores; i++) {
> > int core_dt_id = i * smt;
>
> ..uh, ok, except for that poorly named variable. But that's because
> this is in the machine type, and it knows it's going to use the same
> ids to give to the core object and to put in the device tree.
>
It is core_id everywhere else.
$ git grep core_id hw/ppc/
hw/ppc/spapr.c: cpu_props->has_core_id = true;
hw/ppc/spapr.c: cpu_props->core_id = i * smt;
hw/ppc/spapr_cpu_core.c: spapr->cores[cc->core_id / smt] = NULL;
hw/ppc/spapr_cpu_core.c: drc =
spapr_dr_connector_by_id(SPAPR_DR_CONNECTOR_TYPE_CPU, cc->core_id);
hw/ppc/spapr_cpu_core.c: index = cc->core_id / smt;
hw/ppc/spapr_cpu_core.c: if (cc->core_id % smt) {
hw/ppc/spapr_cpu_core.c: error_setg(&local_err, "invalid core id %d\n",
cc->core_id);
hw/ppc/spapr_cpu_core.c: index = cc->core_id / smt;
hw/ppc/spapr_cpu_core.c: error_setg(&local_err, "core id %d out of
range", cc->core_id);
hw/ppc/spapr_cpu_core.c: error_setg(&local_err, "core %d already
populated", cc->core_id);
$ git grep core_dt_id hw/ppc/
hw/ppc/spapr.c: int core_dt_id = i * smt;
hw/ppc/spapr.c:
SPAPR_DR_CONNECTOR_TYPE_CPU, core_dt_id);
hw/ppc/spapr.c: object_property_set_int(core, core_dt_id,
CPU_CORE_PROP_CORE_ID,
I got confused because the current code still puts cpu_dt_id of thread0 in the
device tree. And since cpu_dt_id is still being computed on cpu_index, it is
a different beast (which needs to be killed since it even crashes simple
hotplug/unplug scenarios).
> > [...]
> > object_property_set_int(core, core_dt_id,
> > CPU_CORE_PROP_CORE_ID,
> > &error_fatal);
> >
> > This patch produces stable_cpu_id in the [0...smt * smp_cores) range. I
> > find it
> > awkward it depends on the host setup.
>
> True. Possibly we should set these as i * (maximum plausible number
> of threads).
>
> The gotcha is that currently we're using the same "dt_id" to control
> KVM's cpu id and that in turn controls the SMT level. That's a poor
> interface on the kernel side (my bad), but we have to live with it
> now. However we could de-couple that KVM id from the core-id. It'd
> no doubt cause some complications with kvm-xics, but we can probably
> handle it.
>
> > I'm suggesting we introduce cc->stable_id to be able to compute a simple
> > stable_cpu_id in the range [0...max_cpus), like x86 and ARM.
>
> I really don't see what properties this is supposed to have that are
> different from the existing core-id.
>
Simplicity of always having CPU0, 1, 2, 3... max_cpus in QEMU, and try
to hide the "poor interface on the kernel side" from the code that
does not need it... but maybe that is not that important.
> >
> > > Instead we should be setting the thread stable ids based on the core
> > > stable id.
> > >
> > > > I think stable_cpu_id is the prerequisite to compute both cpu_dt_id and
> > > > instance_id.
> > > >
> > > > Makes sense ?
> > > >
> > > > > + if (cs->has_stable_cpu_id) {
> > > > > + cs->stable_cpu_id = cc->core_id + i;
> > > > > + }
> > > > > snprintf(id, sizeof(id), "thread[%d]", i);
> > > > > object_property_add_child(OBJECT(sc), id, obj, &local_err);
> > > > > if (local_err) {
> > > >
> > >
> >
>
>
>
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