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[Xen-bugs] [Bug 659] New: only one CPU is detected when dom0 boots up

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Subject: [Xen-bugs] [Bug 659] New: only one CPU is detected when dom0 boots up
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Date: Fri, 26 May 2006 13:36:18 -0700
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           Summary: only one CPU is detected when dom0 boots up
           Product: Xen
           Version: unstable
          Platform: Other
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Guest-OS
        AssignedTo: xen-bugs@xxxxxxxxxxxxxxxxxxx
        ReportedBy: ping.y.yu@xxxxxxxxx
                CC: xiao.zhang@xxxxxxxxx

Buildingx en0 kernel with bulidconfig/linux-defconfig_xen0_x86_64
orbulidconfig/linux-defconfig_xen0_x86_64, with "CONFIG_SMP=y". When dom0
boots up, /proc/cpuinfo will show only one CPU for SMP. Howwever, "uname -a"
will show the kernel is SMP.

After investigation, I found change set 10139 cause the problem.

some discuss in xen-devel is attached.

On 26 May 2006, at 00:22, Yu, Ping Y wrote:

> I notice that it is caused by change set 10139, then does it mean that 
> we have
> to configure CPU hot plug to start multiple CPUs in the future?

It's needed for domU's. Dom0 can bring up SMP without hotplug 

  -- Keir

>-----Original Message-----
>From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
>[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Yu, Ping Y
>Sent: 2006å¹´5æ??25æ?¥ 16:01
>To: Ryan Harper
>Cc: xen-devel@xxxxxxxxxxxxxxxxxxx; Zheng, Jeff
>Subject: RE: [Xen-devel] only one CPU is detected when dom0 boots up
>Thanks a lot. It works! But the question remains that why change set 10033
>could bring up multiple CPUs without hotplug.
>I notice that there is no change in build configuration since 9980.
>>-----Original Message-----
>>From: Ryan Harper [mailto:ryanh@xxxxxxxxxx]
>>Sent: 2006å¹´5æ??25æ?¥ 10:44
>>To: Yu, Ping Y
>>Cc: Zheng, Jeff; xen-devel@xxxxxxxxxxxxxxxxxxx
>>Subject: Re: [Xen-devel] only one CPU is detected when dom0 boots up
>>* Yu, Ping Y <ping.y.yu@xxxxxxxxx> [2006-05-25 11:59]:
>>> Harper,
>>> You are right! The default build configuration linux-defconfig_xen0_x86_64/
>>>  linux-defconfig_xen0_x86_32 is UP, and we have manually changed the default
>>> configure to make it SMP. We noticed that "uname -a" shows the dom0's kernel
>>>  SMP, but the problem is that only one CPU is found when dom0 boots up.
>>> With the same change, we know at least change set 10033 is OK to boot with
>>> multiple CPUs.
>>Make sure CONFIG_HOTPLUG_CPU is also enabled.  After having both
>>xm vcpu-set 0 2
>>replacing 2 with however many cpu's you think dom0 should have.
>>Ryan Harper
>>Software Engineer; Linux Technology Center
>>IBM Corp., Austin, Tx
>>(512) 838-9253   T/L: 678-9253

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