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

[David Gibson]

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.

> 
> [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);

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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