Re: [boost] [atomic] comments

Subject: Re: [boost] [atomic] comments
From: Domagoj Saric (domagoj.saric_at_[hidden])
Date: 2011-10-28 11:12:55

On 21.10.2011. 13:06, Tim Blechmann wrote:
>>> compile-time vs run-time dispatching:
>>> some instructions are not available on every CPU of a specific
>>> architecture. e.g. cmpxchg8b or cmpxchg16b are not available on all
>>> ia32/x86_64 cpus. i would appreciate if these instructions would not be
>>> used before performing a CPUID check, whether these instructions are
>>> really available (at least in a legacy mode)
>>
>> the correct way to do that is to have different libraries for
>> sub-architectures and have the runtime- linker decide... this requires
>> infrastructure not present in boost
>
> it would be equally correct to have something like:
> static bool has_cmpxchg16b = query_cpuid_for_cmpxchg16b()
>
> if (has_cmpxchg16b)
>      use_cmpxchg16b();
> else
>      use_fallback();
>
> less bloat and prbly only a minor performance hit ;)

cmpxchg8b is available since the original Pentium. Preferably dynamic support 
for such ancient hardware, if supported at all, should not be on by default (by 
forcing dynamic dispatching on everyone).

-- 
"What Huxley teaches is that in the age of advanced technology, spiritual
devastation is more likely to come from an enemy with a smiling face than
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