linux-kernel - Re: Question with maxcpus= parameter.

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Message-ID: <564062CE.90106@oracle.com>
Date:	Mon, 9 Nov 2015 17:09:34 +0800
From:	Zhenzhong Duan <zhenzhong.duan@...cle.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Ashok Raj <ashok.raj@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Feng Jin <joe.jin@...cle.com>
Subject: Re: Question with maxcpus= parameter.

在 2015/11/9 14:12, Yinghai Lu 写道:
> On Sun, Nov 8, 2015 at 9:47 PM, Zhenzhong Duan
> <zhenzhong.duan@...cle.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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