Re: [Qemu-devel] [RFC v3 PATCH 14/14] target-i386: Generate fences for x86

[Paolo Bonzini]

On 21/06/2016 18:23, Richard Henderson wrote:
> On 06/21/2016 09:12 AM, Paolo Bonzini wrote:
>>
>>
>> On 21/06/2016 17:57, Richard Henderson wrote:
>>>>>
>>>>>                  || (prefixes & PREFIX_LOCK)) {
>>>>>                  goto illegal_op;
>>>>>              }
>>>>> +            tcg_gen_mb(TCG_MO_ST_ST | TCG_BAR_SC);
>>>>>              break;
>>>>>          case 0xe8 ... 0xef: /* lfence */
>>>>> +            tcg_gen_mb(TCG_MO_LD_LD | TCG_BAR_SC);
>>>>> +            break;
>>>>
>>>> These are unnecessary.  On the other hand, _each and every load_
>>>> must be
>>>> followed by a LD_LD | LD_ST barrier, and each and every store must be
>>>> preceded by a LD_ST | ST_ST barrier.
>>>
>>> They're not unnecessary if we (1) add those barriers for normal loads
>>> and stores and (2) omit them from the non-temporal loads and stores.
>>
>> When does TCG generate non-temporal loads and stores?
> 
> I was talking about the guest non-temporal loads and stores.

Oh, you're right---sorry, I confused target-i386 and tcg/i386.

Thanks,

Paolo