boot_cpu_data differs between Xen hypervisor boot and normal pv_ops kernel boot

boot_cpu_data differs between Xen hypervisor boot and normal pv_ops kernel boot

[Naresh Rapolu]

Hello,

After booting  the  xen-stable 2.6.32.10 pv_ops kernel from jeremy git 
tree  with Xen-4.0.0-rc8 installed,
dmesg | grep PMU  shows :

Performance Events : unsupported p6 CPU model 26 no PMU driver, software 
events only.
PMU:oprofile: found i386/core_i7.

If I boot the same compiled kernel, without Xen installed, dmesg | grep 
PMU shows :
Performance Events : Nehalem/Corei7 events, Intel PMU driver.
PMU:oprofile: found i386/core_i7.


When I looked into the source code,  arch/x86/kernel/cpu/perf_event.c,   
at run-time boot_cpu_data  structure seems to differ  in these two forms 
of booting.
Due to this, Iam not able to use the hardware performance counters in  
my Xeon 5530 processor  as  hardware events(cache-misses etc) are being 
disabled.

Is there any reason for this ?

Any help is appreciated.
Thanks,
Naresh Rapolu.

Re: boot_cpu_data differs between Xen hypervisor boot and normal pv_ops kernel boot

[Pasi Kärkkäinen]

On Wed, Mar 31, 2010 at 11:29:04AM -0400, Naresh Rapolu wrote:
> Hello,
>
> After booting  the  xen-stable 2.6.32.10 pv_ops kernel from jeremy git  
> tree  with Xen-4.0.0-rc8 installed,
> dmesg | grep PMU  shows :
>
> Performance Events : unsupported p6 CPU model 26 no PMU driver, software  
> events only.
> PMU:oprofile: found i386/core_i7.
>
> If I boot the same compiled kernel, without Xen installed, dmesg | grep  
> PMU shows :
> Performance Events : Nehalem/Corei7 events, Intel PMU driver.
> PMU:oprofile: found i386/core_i7.
>
>
> When I looked into the source code,  arch/x86/kernel/cpu/perf_event.c,    
> at run-time boot_cpu_data  structure seems to differ  in these two forms  
> of booting.
> Due to this, Iam not able to use the hardware performance counters in   
> my Xeon 5530 processor  as  hardware events(cache-misses etc) are being  
> disabled.
>
> Is there any reason for this ?
>

I think only xen/stable-2.6.31.x tree currently has power mgmt stuff included.

-- Pasi

Re: boot_cpu_data differs between Xen hypervisor boot and normal pv_ops kernel boot

[Naresh Rapolu]

Thanks Pasi,

But I am concerned about the Performance Monitoring Unit (PMU).  Not 
sure if it has any link to power mgmt unit.  Xen while booting believes  
Xeon 5530 is in the P6 category and hence does not detect the Intel PMU 
driver, thereby hindering  Oprofile to use the performance counters.  
This does not happen if I boot the kernel normally without Xen. 

In  2.6.31.12  , the file for the same is  
arch/x86/kernel/cpu/perf_counters.c  , but  dmesg doesnt show any 
printk  messages from this file when I boot with  xen-3.4.2.   Does Xen 
even consider setting up the performance counters at boot time ?   Did 
anyone successfully use  Oprofile in  2.6.31 kernels for hardware 
performance events ( cache-misses ) etc ?

Iam using ubuntu 8.04 LTS... Does it depend on the OS ?  Can someone 
familiar with the boot code help me please !

Thanks,
Naresh Rapolu.

Pasi Kärkkäinen wrote:
> On Wed, Mar 31, 2010 at 11:29:04AM -0400, Naresh Rapolu wrote:
>   
>> Hello,
>>
>> After booting  the  xen-stable 2.6.32.10 pv_ops kernel from jeremy git  
>> tree  with Xen-4.0.0-rc8 installed,
>> dmesg | grep PMU  shows :
>>
>> Performance Events : unsupported p6 CPU model 26 no PMU driver, software  
>> events only.
>> PMU:oprofile: found i386/core_i7.
>>
>> If I boot the same compiled kernel, without Xen installed, dmesg | grep  
>> PMU shows :
>> Performance Events : Nehalem/Corei7 events, Intel PMU driver.
>> PMU:oprofile: found i386/core_i7.
>>
>>
>> When I looked into the source code,  arch/x86/kernel/cpu/perf_event.c,    
>> at run-time boot_cpu_data  structure seems to differ  in these two forms  
>> of booting.
>> Due to this, Iam not able to use the hardware performance counters in   
>> my Xeon 5530 processor  as  hardware events(cache-misses etc) are being  
>> disabled.
>>
>> Is there any reason for this ?
>>
>>     
>
> I think only xen/stable-2.6.31.x tree currently has power mgmt stuff included.
>
> -- Pasi
>
>
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> http://lists.xensource.com/xen-devel
>   

Re: boot_cpu_data differs between Xen hypervisor boot and normal pv_ops kernel boot

[Jeremy Fitzhardinge]

On 03/31/2010 08:29 AM, Naresh Rapolu wrote:
>
> When I looked into the source code,  
> arch/x86/kernel/cpu/perf_event.c,   at run-time boot_cpu_data  
> structure seems to differ  in these two forms of booting.
> Due to this, Iam not able to use the hardware performance counters in  
> my Xeon 5530 processor  as  hardware events(cache-misses etc) are 
> being disabled.
>
> Is there any reason for this ?

The PMU hardware features are not virtualized, and are not available to 
guest domains.  I don't think Xen has much of a useful API to expose 
these features, though oprofile was working at one point.

I agree it would be very useful to work out how to get good "perf" 
support in a Xen domain.

(Stephen: It might be an interesting SoC project.)

     J