Re: Xen 4.3 development update RC2 imminent

[George Dunlap <george.dunlap@eu.citrix.com>]

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On 23/05/13 15:26, George Dunlap wrote:
> On 23/05/13 15:17, Fabio Fantoni wrote:
>> Il 23/05/2013 12:54, George Dunlap ha scritto:
>>> On 23/05/13 11:39, Andrew Cooper wrote:
>>>> On 23/05/13 11:36, Fabio Fantoni wrote:
>>>>> Il 23/05/2013 09:39, Jan Beulich ha scritto:
>>>>>>>>> On 22.05.13 at 18:54, George Dunlap 
>>>>>>>>> <george.dunlap@eu.citrix.com> wrote:
>>>>>>> On 22/05/13 17:30, Pasi Kärkkäinen wrote:
>>>>>>>> On Wed, May 22, 2013 at 04:05:27PM +0100, George Dunlap wrote:
>>>>>>>> Hmm, for testing, can we use cpuid to mask out SSE,
>>>>>>>> and then try qxl ?
>>>>>>> That had occurred to me -- Andrew / Jan, do you know which flag 
>>>>>>> might
>>>>>>> disable this particular instruction?
>>>>>>>
>>>>>>> I guess we could try just disabling all the SSE instructions.
>>>>>> movdqu is an SSE2 instruction, so disabling bit 26 of CPUID EDX
>>>>>> output to EAX=1 input.
>>>>> Can you explain better please?
>>>>> Should I add this to test it?
>>>>> cpuid="host,sse=0,sse2=0,ssse3=0,sse4_1=0,sse4_2=0,eax=1"
>>>> It will likely not work.  SSE2 is an architectural requirement for 
>>>> 64bit.
>>>>
>>>> It means that 64bit code may assume the presence of SSE2. Xen amongst
>>>> other software does make this assumption.
>>>
>>> It might work if he's using 32-bit.
>>>
>>> Fabio, as I said in my initial e-mail, you need to:
>>>
>>> 1. Run "cat /proc/cpuinfo" on your dom0
>>> 2. Look at the line that says "features:"
>>> 3. Find all the things that contain "sse" > 2 (sse2, ssse3, &c)
>>> 4. Set them to 0 in the "cpuid" field like above.
>>>
>>> Every processor will be a bit different -- you can't just copy mine 
>>> and expect it to work.
>>>
>>> Don't include "eax=1" -- Jan is thinking of a different interface.
>>>
>>>  -George
>> Tried with Raring (ubuntu 13.04) 32bit...
>> in cfg:
>> cpuid="host,sse=0,sse2=0,ssse3=0,sse4_1=0,sse4_2=0"
>>
>> # xl create /etc/xen/RARING.cfg
>> Parsing config from /etc/xen/RARING.cfg
>> while parsing CPUID flag: "sse4_1=0":
>>   error #2: unknown CPUID flag name
>> while parsing CPUID flag: "sse4_2=0":
>>   error #2: unknown CPUID flag name
>
> Right -- in that case this is a minor bug in libxl.  (Actually I got 
> the same result, I just didn't notice the error messages -- sorry 
> about that.)

Actually it's not a bug per se; libxl apparently just calls these sse4.1 
and sse4.2 respectively.

  -George


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