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Re: [libvirt] [Resending][PATCH v2 2/2] x86: Allow sysinfo to fall back on /proc/cpuinfo if demidecode is absent



Hi Daniel,
Thank you for taking a look.

On 03/14/2012 02:29 PM, Daniel Veillard wrote:
> On Tue, Mar 13, 2012 at 11:10:16AM +0530, Prerna Saxena wrote:
>> From: Prerna Saxena <prerna linux vnet ibm com>
>> Date: Tue, 13 Mar 2012 15:33:43 +0530
>> Subject: [PATCH 2/2] Sysinfo : Allow x86 to fetch sysinfo from 
>>  /proc/cpuinfo in the event 'dmidecode' is absent in the system.
>>
>> Until now, libvirt on x86 flags an error message if dmidecode is not
>> found. With this patch, the following is a sample output on x86 when
>> dmidecode is absent:
>>
>> virsh # sysinfo
>> <sysinfo type='smbios'>
>>   <processor>
>>     <entry name='socket_destination'>0</entry>
>>     <entry name='type'>Intel(R) Xeon(R) CPU X5570  @ 2.93GHz</entry>
>>     <entry name='family'>6</entry>
>>     <entry name='manufacturer'>GenuineIntel</entry>
>>   </processor>
>>   <processor>
>>     <entry name='socket_destination'>1</entry>
>>     <entry name='type'>Intel(R) Xeon(R) CPU X5570  @ 2.93GHz</entry>
>>     <entry name='family'>6</entry>
>>     <entry name='manufacturer'>GenuineIntel</entry>
>>   </processor>
>>   ... (listing for all online CPUs)
>> </sysinfo>
>>
>> Based on suggestion from Eric:
>> (http://www.redhat.com/archives/libvir-list/2012-February/msg00509.html)
>>
>> Acked-by: Daniel P Berrange <berrange redhat com>
>> Signed-off-by: Prerna Saxena <prerna linux vnet ibm com>
>> ---
>>  src/util/sysinfo.c |   97 +++++++++++++++++++++++++++++++++++++++++++++++++--
>>  1 files changed, 93 insertions(+), 4 deletions(-)
>> 
>> ... [snip]..
> 
>   Hi Prerna,
> 
> that sounds like a good idea, and the patch seems to work but I have
> doubt with the usefulness in its current form. Let me explain:
> 
> with dmidecode available on my system I get:
> 
>   ...
>   <processor>
>     <entry name='socket_destination'>Socket 775</entry>
>     <entry name='type'>Central Processor</entry>
>     <entry name='family'>Other</entry>
>     <entry name='manufacturer'>Intel</entry>
>     <entry name='signature'>Type 0, Family 6, Model 15, Stepping
> 11</entry>
>     <entry name='version'>Intel(R) Core(TM)2 Duo CPU     E6550  @
> 2.33GHz</entry>
>     <entry name='external_clock'>333 MHz</entry>
>     <entry name='max_speed'>4000 MHz</entry>
>     <entry name='status'>Populated, Enabled</entry>
>   </processor>
>   ...
> 
> without dmidecode and your patch plugged in I get
> 
>   <processor>
>     <entry name='socket_destination'>0</entry>
>     <entry name='type'>Intel(R) Core(TM)2 Duo CPU     E6550  @
> 2.33GHz</entry>
>     <entry name='family'>6</entry>
>     <entry name='manufacturer'>GenuineIntel</entry>
>   </processor>
>   <processor>
>     <entry name='socket_destination'>1</entry>
>     <entry name='type'>Intel(R) Core(TM)2 Duo CPU     E6550  @
> 2.33GHz</entry>
>     <entry name='family'>6</entry>
>     <entry name='manufacturer'>GenuineIntel</entry>
>   </processor>
> 
> so basically we get informations, some are available in both case but
> differently, and worse, in the fallback case we get 2 physical processor
> entries (I have only one) which is of course different from the single
> processor that we get with dmidecode.
> 
>   So 1/ is seems to me the fallback data can't be parsed
> programmatically as a replacement of the original ones
>      2/ the data may be misunderstood and lead to erroneous
> decision for example a schedule may start to stack 2 time more
> load on my machine based on the difference of report.
> 
>  So I'm a bit worried about applying it as-is, I'm afraid we need
> to reconcile the output (as much as possible considering there
> is less data) between both cases.
> 

Thanks for pointing this out. I investigated this discrepancy, and
discovered that 'dmidecode' presents a listing of processor *cores*.
However, for /proc/cpuinfo, all hardware threads in a processor show up
as independent processors. So, while dmidecode correctly reads that my
system has a single core, /proc/cpuinfo reports two hardware threads in
the core as two independent logical CPUs.
To sort this out, one alternative would be to parse the physical_id in
/proc/cpuinfo -- this would be identical for all logical processors in a
given core, and thus can be used to report the number of cores in the
system. Will send a modified patch asap.

>   That said I think patch 1/2 looks fine to me, and could probably be
> applied as-is,
> 

Thanks! Would you want to apply it as-is, or shall I send a rebased
version ?

> Daniel
> 

Regards,
-- 
Prerna Saxena

Linux Technology Centre,
IBM Systems and Technology Lab,
Bangalore, India


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