Re: [Xen-devel] [PATCH] xen: Add command line option to enable ASID support -- on by default

[Keir Fraser <keir@xxxxxxx>]

On 07/03/2012 18:14, "George Dunlap" <george.dunlap@xxxxxxxxxx> wrote:

> On Wed, 2012-03-07 at 18:07 +0000, Keir Fraser wrote:
>> On 07/03/2012 17:58, "George Dunlap" <george.dunlap@xxxxxxxxxxxxx> wrote:
>> 
>>> Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
>> 
>> Why would you want to be able to disable the feature?
> 
> Well at very least to measure the performance benefit (or overhead) of
> using the feature.  There may be hardware in the future where ASIDs may
> cause problems; who knows.
> 
> AFAICT this isn't documented anywhere, so if you really don't want Yet
> Another Option, we could probably get rid of it from the XenServer
> patchqueue.  But I didn't see any harm in it; and you never know when
> the flexibility of disabling something without recompiling will come in
> handy.

Okay, I applied it. I also moved the implementation into hvm/asid.c by the
way -- your patch was unnecessarily AMD-specific.

xen-unstable:24986

 -- Keir

>  -George
> 
>> 
>>  -- Keir
>> 
>>> diff --git a/xen/arch/x86/hvm/svm/asid.c b/xen/arch/x86/hvm/svm/asid.c
>>> --- a/xen/arch/x86/hvm/svm/asid.c
>>> +++ b/xen/arch/x86/hvm/svm/asid.c
>>> @@ -24,12 +24,16 @@
>>>  #include <asm/amd.h>
>>>  #include <asm/hvm/nestedhvm.h>
>>>  
>>> +/* Xen command-line option to enable ASIDs */
>>> +static int opt_asid_enabled = 1;
>>> +boolean_param("asid", opt_asid_enabled);
>>> +
>>>  void svm_asid_init(struct cpuinfo_x86 *c)
>>>  {
>>>      int nasids = 0;
>>>  
>>>      /* Check for erratum #170, and leave ASIDs disabled if it's present. */
>>> -    if ( !cpu_has_amd_erratum(c, AMD_ERRATUM_170) )
>>> +    if ( opt_asid_enabled && !cpu_has_amd_erratum(c, AMD_ERRATUM_170) )
>>>          nasids = cpuid_ebx(0x8000000A);
>>>  
>>>      hvm_asid_init(nasids);
>>> 
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>>> http://lists.xen.org/xen-devel
>> 
>> 
> 
> 



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