Re: [PATCH 1/2] spapr: number of SMP sockets must be equal to NUMA nodes

[Daniel Henrique Barboza]

On 3/29/21 8:51 PM, Igor Mammedov wrote:
> On Tue, 23 Mar 2021 12:03:58 +1100
> David Gibson <david@gibson.dropbear.id.au> wrote:
>
> > On Fri, Mar 19, 2021 at 03:34:52PM -0300, Daniel Henrique Barboza wrote:
> > > Kernel commit 4bce545903fa ("powerpc/topology: Update
> > > topology_core_cpumask") cause a regression in the pseries machine when
> > > defining certain SMP topologies [1]. The reasoning behind the change is
> > > explained in kernel commit 4ca234a9cbd7 ("powerpc/smp: Stop updating
> > > cpu_core_mask"). In short, cpu_core_mask logic was causing troubles with
> > > large VMs with lots of CPUs and was changed by cpu_cpu_mask because, as
> > > far as the kernel understanding of SMP topologies goes, both masks are
> > > equivalent.
> > >
> > > Further discussions in the kernel mailing list [2] shown that the
> > > powerpc kernel always considered that the number of sockets were equal
> > > to the number of NUMA nodes. The claim is that it doesn't make sense,
> > > for Power hardware at least, 2+ sockets being in the same NUMA node. The
> > > immediate conclusion is that all SMP topologies the pseries machine were
> > > supplying to the kernel, with more than one socket in the same NUMA node
> > > as in [1], happened to be correctly represented in the kernel by
> > > accident during all these years.
> > >
> > > There's a case to be made for virtual topologies being detached from
> > > hardware constraints, allowing maximum flexibility to users. At the same
> > > time, this freedom can't result in unrealistic hardware representations
> > > being emulated. If the real hardware and the pseries kernel don't
> > > support multiple chips/sockets in the same NUMA node, neither should we.
> > >
> > > Starting in 6.0.0, all sockets must match an unique NUMA node in the
> > > pseries machine. qtest changes were made to adapt to this new
> > > condition.
> >
> > Oof.  I really don't like this idea.  It means a bunch of fiddly work
> > for users to match these up, for no real gain.  I'm also concerned
> > that this will require follow on changes in libvirt to not make this a
> > really cryptic and irritating point of failure.
>
> yes, it is annoying to users but we were very slowly tightening limitations
> on numa path, especially if it causes problems on guest side when user
> specify nonsense configs (and suspect there are few things to enforce in
> generic numa code left (currently just warnings)). So it's nothing new.

Do you mind elaborating a bit on the 'nonsense configs' bit? Do you mean
configs that are unrealistic because it's uncompliant with ACPI? I always
thought that all possible SMP/NUMA topologies QEMU allows were ACPI/x86
compliant.

If both x86 and PowerPC have restrictions in common we might want to consider
putting this code in a common helper/place.


> So if limit applies to new machine type it should be fine (i.e. no existing
> VMs will suffer). Later on we can deprecate invalid configurations altogether
> and just error out.

hmmm I'm not warning the user about the deprecated topologies in existing
guests in this patch. I guess it doesn't hurt to add a warning for existing
VMs.



Thanks,


DHB


>   
> > > [1] https://bugzilla.redhat.com/1934421
> > > [2] 
> > > https://lore.kernel.org/linuxppc-dev/daa5d05f-dbd0-05ad-7395-5d5a3d364fc6@gmail.com/
> > >
> > > CC: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> > > CC: Cédric Le Goater <clg@kaod.org>
> > > CC: Igor Mammedov <imammedo@redhat.com>
> > > CC: Laurent Vivier <lvivier@redhat.com>
> > > CC: Thomas Huth <thuth@redhat.com>
> > > Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
> > > ---
> > >   hw/ppc/spapr.c                 |  3 ++
> > >   hw/ppc/spapr_numa.c            |  7 +++++
> > >   include/hw/ppc/spapr.h         |  1 +
> > >   tests/qtest/cpu-plug-test.c    |  4 +--
> > >   tests/qtest/device-plug-test.c |  9 +++++-
> > >   tests/qtest/numa-test.c        | 52 ++++++++++++++++++++++++++++------
> > >   6 files changed, 64 insertions(+), 12 deletions(-)
> > >
> > > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > > index d56418ca29..745f71c243 100644
> > > --- a/hw/ppc/spapr.c
> > > +++ b/hw/ppc/spapr.c
> > > @@ -4611,8 +4611,11 @@ DEFINE_SPAPR_MACHINE(6_0, "6.0", true);
> > >    */
> > >   static void spapr_machine_5_2_class_options(MachineClass *mc)
> > >   {
> > > +    SpaprMachineClass *smc = SPAPR_MACHINE_CLASS(mc);
> > > +
> > >       spapr_machine_6_0_class_options(mc);
> > >       compat_props_add(mc->compat_props, hw_compat_5_2, hw_compat_5_2_len);
> > > +    smc->pre_6_0_smp_topology = true;
> > >   }
> > >   
> > >   DEFINE_SPAPR_MACHINE(5_2, "5.2", false);
> > > diff --git a/hw/ppc/spapr_numa.c b/hw/ppc/spapr_numa.c
> > > index 779f18b994..0ade43dd79 100644
> > > --- a/hw/ppc/spapr_numa.c
> > > +++ b/hw/ppc/spapr_numa.c
> > > @@ -163,6 +163,13 @@ void spapr_numa_associativity_init(SpaprMachineState 
> > > *spapr,
> > >       int i, j, max_nodes_with_gpus;
> > >       bool using_legacy_numa = spapr_machine_using_legacy_numa(spapr);
> > >   
> > > +    if (!smc->pre_6_0_smp_topology &&
> > > +        nb_numa_nodes != machine->smp.sockets) {
> > > +        error_report("Number of CPU sockets must be equal to the number "
> > > +                     "of NUMA nodes");
> > > +        exit(EXIT_FAILURE);
> > > +    }
> > > +
> > >       /*
> > >        * For all associativity arrays: first position is the size,
> > >        * position MAX_DISTANCE_REF_POINTS is always the numa_id,
> > > diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> > > index 47cebaf3ac..98dc5d198a 100644
> > > --- a/include/hw/ppc/spapr.h
> > > +++ b/include/hw/ppc/spapr.h
> > > @@ -142,6 +142,7 @@ struct SpaprMachineClass {
> > >       hwaddr rma_limit;          /* clamp the RMA to this size */
> > >       bool pre_5_1_assoc_refpoints;
> > >       bool pre_5_2_numa_associativity;
> > > +    bool pre_6_0_smp_topology;
> > >   
> > >       bool (*phb_placement)(SpaprMachineState *spapr, uint32_t index,
> > >                             uint64_t *buid, hwaddr *pio,
> > > diff --git a/tests/qtest/cpu-plug-test.c b/tests/qtest/cpu-plug-test.c
> > > index a1c689414b..946b9129ea 100644
> > > --- a/tests/qtest/cpu-plug-test.c
> > > +++ b/tests/qtest/cpu-plug-test.c
> > > @@ -118,8 +118,8 @@ static void add_pseries_test_case(const char *mname)
> > >       data->machine = g_strdup(mname);
> > >       data->cpu_model = "power8_v2.0";
> > >       data->device_model = g_strdup("power8_v2.0-spapr-cpu-core");
> > > -    data->sockets = 2;
> > > -    data->cores = 3;
> > > +    data->sockets = 1;
> > > +    data->cores = 6;
> > >       data->threads = 1;
> > >       data->maxcpus = data->sockets * data->cores * data->threads;
> > >   
> > > diff --git a/tests/qtest/device-plug-test.c b/tests/qtest/device-plug-test.c
> > > index 559d47727a..dd7d8268d2 100644
> > > --- a/tests/qtest/device-plug-test.c
> > > +++ b/tests/qtest/device-plug-test.c
> > > @@ -91,7 +91,14 @@ static void test_spapr_cpu_unplug_request(void)
> > >   {
> > >       QTestState *qtest;
> > >   
> > > -    qtest = qtest_initf("-cpu power9_v2.0 -smp 1,maxcpus=2 "
> > > +    /*
> > > +     * Default smp settings will prioritize sockets over cores and
> > > +     * threads, so '-smp 2,maxcpus=2' will add 2 sockets. However,
> > > +     * the pseries machine requires a NUMA node for each socket
> > > +     * (since 6.0.0). Specify sockets=1 to make life easier.
> > > +     */
> > > +    qtest = qtest_initf("-cpu power9_v2.0 "
> > > +                        "-smp 1,maxcpus=2,threads=1,cores=2,sockets=1 "
> > >                           "-device 
> > > power9_v2.0-spapr-cpu-core,core-id=1,id=dev0");
> > >   
> > >       /* similar to test_pci_unplug_request */
> > > diff --git a/tests/qtest/numa-test.c b/tests/qtest/numa-test.c
> > > index dc0ec571ca..bb13f7131b 100644
> > > --- a/tests/qtest/numa-test.c
> > > +++ b/tests/qtest/numa-test.c
> > > @@ -24,9 +24,17 @@ static void test_mon_explicit(const void *data)
> > >       QTestState *qts;
> > >       g_autofree char *s = NULL;
> > >       g_autofree char *cli = NULL;
> > > +    const char *arch = qtest_get_arch();
> > > +
> > > +    if (g_str_equal(arch, "ppc64")) {
> > > +        cli = make_cli(data, "-smp 8,threads=1,cores=4,sockets=2 "
> > > +                             "-numa node,nodeid=0,memdev=ram,cpus=0-3 "
> > > +                             "-numa node,nodeid=1,cpus=4-7");
> > > +    } else {
> > > +        cli = make_cli(data, "-smp 8 -numa node,nodeid=0,memdev=ram,cpus=0-3 "
> > > +                             "-numa node,nodeid=1,cpus=4-7");
> > > +    }
> > >   
> > > -    cli = make_cli(data, "-smp 8 -numa node,nodeid=0,memdev=ram,cpus=0-3 "
> > > -                         "-numa node,nodeid=1,cpus=4-7");
> > >       qts = qtest_init(cli);
> > >   
> > >       s = qtest_hmp(qts, "info numa");
> > > @@ -57,10 +65,18 @@ static void test_mon_partial(const void *data)
> > >       QTestState *qts;
> > >       g_autofree char *s = NULL;
> > >       g_autofree char *cli = NULL;
> > > +    const char *arch = qtest_get_arch();
> > > +
> > > +    if (g_str_equal(arch, "ppc64")) {
> > > +        cli = make_cli(data, "-smp 8,threads=1,cores=4,sockets=2 "
> > > +                             "-numa node,nodeid=0,memdev=ram,cpus=0-1 "
> > > +                             "-numa node,nodeid=1,cpus=4-5 ");
> > > +    } else {
> > > +        cli = make_cli(data, "-smp 8 "
> > > +                             "-numa node,nodeid=0,memdev=ram,cpus=0-1 "
> > > +                             "-numa node,nodeid=1,cpus=4-5 ");
> > > +    }
> > >   
> > > -    cli = make_cli(data, "-smp 8 "
> > > -                   "-numa node,nodeid=0,memdev=ram,cpus=0-1 "
> > > -                   "-numa node,nodeid=1,cpus=4-5 ");
> > >       qts = qtest_init(cli);
> > >   
> > >       s = qtest_hmp(qts, "info numa");
> > > @@ -85,9 +101,17 @@ static void test_query_cpus(const void *data)
> > >       QObject *e;
> > >       QTestState *qts;
> > >       g_autofree char *cli = NULL;
> > > +    const char *arch = qtest_get_arch();
> > > +
> > > +    if (g_str_equal(arch, "ppc64")) {
> > > +        cli = make_cli(data, "-smp 8,threads=1,cores=4,sockets=2 "
> > > +                             "-numa node,memdev=ram,cpus=0-3 "
> > > +                             "-numa node,cpus=4-7");
> > > +    } else {
> > > +        cli = make_cli(data, "-smp 8 -numa node,memdev=ram,cpus=0-3 "
> > > +                             "-numa node,cpus=4-7");
> > > +    }
> > >   
> > > -    cli = make_cli(data, "-smp 8 -numa node,memdev=ram,cpus=0-3 "
> > > -                         "-numa node,cpus=4-7");
> > >       qts = qtest_init(cli);
> > >       cpus = get_cpus(qts, &resp);
> > >       g_assert(cpus);
> > > @@ -177,7 +201,7 @@ static void spapr_numa_cpu(const void *data)
> > >       QTestState *qts;
> > >       g_autofree char *cli = NULL;
> > >   
> > > -    cli = make_cli(data, "-smp 4,cores=4 "
> > > +    cli = make_cli(data, "-smp 4,threads=1,cores=2,sockets=2 "
> > >           "-numa node,nodeid=0,memdev=ram -numa node,nodeid=1 "
> > >           "-numa cpu,node-id=0,core-id=0 "
> > >           "-numa cpu,node-id=0,core-id=1 "
> > > @@ -554,7 +578,17 @@ int main(int argc, char **argv)
> > >   
> > >       g_test_init(&argc, &argv, NULL);
> > >   
> > > -    qtest_add_data_func("/numa/mon/cpus/default", args, test_def_cpu_split);
> > > +    /*
> > > +     * Starting on 6.0.0, for the pseries machine, '-smp 8' will only work
> > > +     * if we have 8 NUMA nodes. If we specify 'smp 8,sockets=2' to match
> > > +     * 2 NUMA nodes, the CPUs will be split as 0123/4567 instead of
> > > +     * 0246/1357 that test_def_cpu_split expects. In short, this test is
> > > +     * no longer valid for ppc64 in 6.0.0.
> > > +     */
> > > +    if (!g_str_equal(arch, "ppc64")) {
> > > +        qtest_add_data_func("/numa/mon/cpus/default", args, 
> > > test_def_cpu_split);
> > > +    }
> > > +
> > >       qtest_add_data_func("/numa/mon/cpus/explicit", args, test_mon_explicit);
> > >       qtest_add_data_func("/numa/mon/cpus/partial", args, test_mon_partial);
> > >       qtest_add_data_func("/numa/qmp/cpus/query-cpus", args, test_query_cpus);