Re: [RFC PATCH] tests/qtest/migration: Add cpu hotplug test

[Igor Mammedov]

On Mon, 13 Jan 2025 18:08:33 -0300
Fabiano Rosas <farosas@suse.de> wrote:

> Bug #2594 is about a failure during migration after a cpu hotplug. Add
> a test that covers that scenario. Start the source with -smp 2 and
> destination with -smp 3, plug one extra cpu to match and migrate.

-smp on target should be the same as on source.
Instead use '-device hotplugged_cpu' with the same args as
in used device_add on target, to account for an extra cpu

> 
> The issue seems to be a mismatch in the number of virtqueues between
> the source and destination due to the hotplug not changing the
> num_queues:
> 
>   get_pci_config_device: Bad config data: i=0x9a read: 4 device: 5
>   cmask: ff wmask: 0 w1cmask:0
> 
> Usage:
> $ QTEST_QEMU_IMG=./qemu-img QTEST_QEMU_BINARY=./qemu-system-x86_64 \
>   ./tests/qtest/migration-test -p /x86_64/migration/hotplug/cpu
> 
> References: https://gitlab.com/qemu-project/qemu/-/issues/2594
> References: https://issues.redhat.com/browse/RHEL-68302
> Signed-off-by: Fabiano Rosas <farosas@suse.de>
> ---
> As you can see there's no fix attached to this. I haven't reached that
> part yet, suggestions welcome =). Posting the test case if anyone
> wants to play with this.
> 
> (if someone at RH is already working on this, that's fine. I'm just
> trying to get some upstream bugs to move)
> ---
>  tests/qtest/migration/misc-tests.c | 76 ++++++++++++++++++++++++++++++
>  1 file changed, 76 insertions(+)
> 
> diff --git a/tests/qtest/migration/misc-tests.c 
> b/tests/qtest/migration/misc-tests.c
> index 6173430748..bde567b124 100644
> --- a/tests/qtest/migration/misc-tests.c
> +++ b/tests/qtest/migration/misc-tests.c
> @@ -251,6 +251,79 @@ static void test_validate_uri_channels_none_set(void)
>      do_test_validate_uri_channel(&args);
>  }
>  
> +static void test_cpu_hotplug_virtqueues(void)
> +{
> +    MigrateStart args = {
> +        .hide_stderr = false,
> +    };
> +    QTestState *from, *to;
> +    g_autofree char *device_virtio_scsi = NULL;
> +    g_autofree char *device_virtio_blk = NULL;
> +    g_autofree char *filename_scsi = g_strdup_printf("%s/qtest_disk0.qcow2", 
> tmpfs);
> +    g_autofree char *filename_blk = g_strdup_printf("%s/qtest_disk1.qcow2", 
> tmpfs);
> +
> +    /*
> +     * Matching the queues between src/dst allows the test to pass.
> +     * Defaults are:
> +     *   virtio-scsi-pci:   #vcpus + 2 queues that are always present.
> +     *   virtio-blk-pci:    same number of queues as vcpus.
> +     * See virtio_pci_optimal_num_queues() for the exact computation.
> +     */
> +    bool match_queues = false;
> +    const char *qs_scsi = "num_queues=5";
> +    const char *qs_blk = "num-queues=3"; /* _ vs. - is not a mistake */
> +
> +    g_assert(mkimg(filename_scsi, "qcow2", 1));
> +    g_assert(mkimg(filename_blk, "qcow2", 1));
> +
> +    device_virtio_scsi = g_strdup_printf(
> +        "-drive id=drive0,if=none,format=qcow2,file=%s "
> +        "-device virtio-scsi-pci,id=scsi0,%s "
> +        "-device scsi-hd,drive=drive0,bus=scsi0.0 ",
> +        filename_scsi, match_queues ? qs_scsi : "");
> +
> +    device_virtio_blk = g_strdup_printf(
> +        "-drive id=drive1,if=none,format=qcow2,file=%s "
> +        "-device virtio-blk-pci,drive=drive1,id=blk0,%s ",
> +        filename_blk, match_queues ? qs_blk : "");
> +
> +    /* The missing cpu will be hotplugged before migration */
> +    args.opts_source = g_strconcat("-smp 2,threads=1,sockets=1,maxcpus=4 ",
> +                                   device_virtio_scsi,
> +                                   device_virtio_blk, NULL);
> +
> +    args.opts_target = g_strconcat("-smp 3,threads=1,sockets=1,maxcpus=4 ",
> +                                   device_virtio_scsi,
> +                                   device_virtio_blk, NULL);
> +
> +    if (migrate_start(&from, &to, "defer", &args)) {
> +        return;
> +    }
> +
> +    g_free((char *)args.opts_source);
> +    g_free((char *)args.opts_target);
> +
> +
> +    migrate_ensure_converge(from);
> +    wait_for_serial("src_serial");
> +
> +    qtest_qmp_assert_success(from, "{ 'execute': 'device_add',"
> +                             "  'arguments': { "
> +                             "    'node-id': 0, 'socket-id': 0,"
> +                             "    'core-id': 2, 'thread-id': 0,"
> +                             "    'id': {},"
> +                             "    'driver': 'qemu64-x86_64-cpu' } }");
> +
> +    migrate_incoming_qmp(to, "tcp:127.0.0.1:0", "{}");
> +
> +    migrate_qmp(from, to, NULL, NULL, "{}");
> +    wait_for_migration_complete(from);
> +
> +    migrate_end(from, to, true);
> +    unlink(filename_scsi);
> +    unlink(filename_blk);
> +}
> +
>  void migration_test_add_misc(MigrationTestEnv *env)
>  {
>      tmpfs = env->tmpfs;
> @@ -279,4 +352,7 @@ void migration_test_add_misc(MigrationTestEnv *env)
>                         test_validate_uri_channels_both_set);
>      migration_test_add("/migration/validate_uri/channels/none_set",
>                         test_validate_uri_channels_none_set);
> +
> +    migration_test_add("/migration/hotplug/cpu/virtqueues",
> +                       test_cpu_hotplug_virtqueues);
>  }