svn commit: r219679 - head/sys/i386/include

[Peter Jeremy]

On 2011-Mar-16 16:34:04 -0400, Jung-uk Kim <jkim at FreeBSD.org> wrote:
>On Wednesday 16 March 2011 01:45 pm, Roman Divacky wrote:
>> if we drop i486 I think it makes sense to require something that
>> has at least SSE2, thus we can have the same expectations as on
>> amd64.

I think it's stil a bit early for that - especially the SSE2 requirement.

>This is a proof-of-concept patch for sys/x86/isa/clock.c:
>
>http://people.freebsd.org/~jkim/clock.diff
>
>You see the complexity, just because I wanted to load 64-bit value 
>atomically... :-(

An alternative approach is to have _fetch_frequency() be
  uint64_t (*_fetch_frequency)(uint64_t *);
if i386 and I486 are defined (otherwise it's just the #define (*(p)))
then initialise it to either atomic_fetch_quad_i386 or
atomic_fetch_quad_i586 as part of the CPU detection process.  This is
the way bcopy() is/was handled on Pentium.

Another approach would be to always have cmpxchg8b instructions
(followed by a suitably large NOP) always inlined in the code and if
it traps, patch the code to call a function that emulates it.

-- 
Peter Jeremy
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