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    SubjectRe: Question with maxcpus= parameter.
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    在 2015/11/9 14:12, Yinghai Lu 写道:
    > On Sun, Nov 8, 2015 at 9:47 PM, Zhenzhong Duan
    > <zhenzhong.duan@oracle.com> wrote:
    >> Tried nr_cpus=4, works.
    >>
    > nr_cpus and maxcpus are different.
    >
    > maxcpus=4 means kernel will only bring up 4 cpus, but other cpus still
    > can be brought up online.
    > if there are more cpu are there according acpi MADT.
    >
    > nr_cpus=4 that means 4 is hard limit, just like you compiled kernel
    > with CONFIG_NR_CPUS=4.
    I know that, what confused me is uek2(2.6.39-400.249.4.el6uek.x86_64)
    works with maxcpus=,
    but uek3(3.8.13-44.1.1.el6uek.x86_64) not when I don't comment out the
    script.
    I have ever suspected uek2 send CPU ADD event for only 4 cpus.
    dyndbg="file kobject_uevent.c +p" is used when debug, vimdiff with both
    dmesg:

    uek2 | uek3
    ......
    PCI: Using configuration type 1 for base
    access | PCI: Using configuration
    type 1 for base access
    kobject: 'node0' (ffffffff81d6c9d0):
    kobject_uevent_env | kobject: 'node0'
    (ffff883f25984410): kobject_uevent_env
    kobject: 'cpu0' (ffff88407ec0b2f8):
    kobject_uevent_env | kobject: 'cpu0'
    (ffff883f7ec0c3d8): kobject_uevent_env
    kobject: 'cpu1' (ffff88407ec2b2f8):
    kobject_uevent_env | kobject: 'cpu1'
    (ffff883f7ec2c3d8): kobject_uevent_env
    ......
    kobject: 'cpu70' (ffff88407f4cb2f8):
    kobject_uevent_env | kobject: 'cpu70'
    (ffff883f7f4cc3d8): kobject_uevent_env
    kobject: 'cpu71' (ffff88407f4eb2f8):
    kobject_uevent_env | kobject: 'cpu71'
    (ffff883f7f4ec3d8): kobject_uevent_env
    ......
    dracut: dracut-004-356.0.1.el6 | dracut:
    dracut-004-356.0.1.el6
    dracut: rd_NO_LUKS: removing cryptoluks
    activation | dracut: rd_NO_LUKS: removing
    cryptoluks activation
    kobject: 'dm_mod' (ffffffffa000e290):
    kobject_uevent_env | kobject: 'dm_mod'
    (ffffffffa000f3b0): kobject_uevent_env
    device-mapper: uevent: version
    1.0.3 |
    device-mapper: uevent: version 1.0.3
    udev: starting version 147 | udev: starting version 147
    ......
    kobject: 'cpu0' (ffff883f0076dc10):
    kobject_uevent_env | kobject: 'cpu0'
    (ffff883f7ec0c3d8): kobject_uevent_env
    kobject: 'cpu1' (ffff883f0076d810):
    kobject_uevent_env | kobject: 'cpu1'
    (ffff883f7ec2c3d8): kobject_uevent_env
    kobject: 'cpu2' (ffff883f0076d410):
    kobject_uevent_env | kobject: 'cpu10'
    (ffff883f7ed4c3d8): kobject_uevent_env
    kobject: 'cpu3' (ffff883f0076d010):
    kobject_uevent_env | kobject: 'cpu11'
    (ffff883f7ed6c3d8): kobject_uevent_env
    kobject: 'id' (ffff883f05716c10):
    kobject_uevent_env | kobject: 'cpu12'
    (ffff883f7ed8c3d8): kobject_uevent_env
    kobject: 'fbcon' (ffff883f05779c10):
    kobject_uevent_env | kobject: 'cpu13'
    (ffff883f7f42c3d8): kobject_uevent_env
    ...... | ...... (total 72 cpus)
    dracut: | dracut:
    dracut: Switching root | dracut: Switching root
    udev: starting version 147 | udev: starting version 147
    kobject: 'cpu0' (ffff883f0076dc10):
    kobject_uevent_env | kobject: 'cpu0'
    (ffff883f7ec0c3d8): kobject_uevent_env
    kobject: 'cpu1' (ffff883f0076d810):
    kobject_uevent_env | kobject: 'cpu1'
    (ffff883f7ec2c3d8): kobject_uevent_env
    kobject: 'cpu2' (ffff883f0076d410):
    kobject_uevent_env | kobject: 'cpu10'
    (ffff883f7ed4c3d8): kobject_uevent_env
    kobject: 'cpu3' (ffff883f0076d010):
    kobject_uevent_env | kobject: 'cpu11'
    (ffff883f7ed6c3d8): kobject_uevent_env
    kobject: 'id' (ffff883f05716c10):
    kobject_uevent_env | kobject: 'cpu12'
    (ffff883f7ed8c3d8): kobject_uevent_env
    kobject: 'fbcon' (ffff883f05779c10):
    kobject_uevent_env | kobject: 'cpu13'
    (ffff883f7f42c3d8): kobject_uevent_env
    ...... | ...... (total 72 cpus)

    I looked at the path to send event at bootup, it's almost same, the
    dmesg confirmed this.
    uek2
    topology_init->arch_register_cpu->register_cpu->sysdev_register->kobject_uevent(&dev->kobj,
    KOBJ_ADD);
    uek3
    topology_init->arch_register_cpu->register_cpu->device_register->kobject_uevent(&dev->kobj,
    KOBJ_ADD);

    But I don't find who send event again after udev start with different
    cpu count.

    thanks
    zduan



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