Re: ZFS committed to the FreeBSD base.

Peter Jeremy <peterjeremy@xxxxxxxxxxxxxxxx> writes:
There's a feature bit (CPUID_CX8) that advertises the availability of
cmpxchg8b (and maybe some related instructions). My pre-MMX 586 has
this bit set so I presume anything later than 486 will support it.
(I'm not sure about the low-end VIA, GEODE etc clones).

The Geode is a 486, and does not support it.

The C3 however is a 586. The C3 Ezra and C3 Samuel / Samuel 2 do not
have CX8. I'm not sure about the C3 Nehemiah, I don't have one
running at the moment.

I agree that GENERIC should run on lowest-common-denominator hardware
(the definition of that is a subject for a different thread). GENERIC
performance could be enhanced by using an indirect call for 8-byte
atomic instructions and selecting between the cmpxchg8b and
alternative implementation as part of the CPU startup (much like
i586_bcopy). If CPU_486 is not defined, you code could inline the
cmpxchg8b-based variant.

Our native atomic operations are all defined as either macros or
static inline functions in machine/atomic.h, so we can easily make
this choice at compile time based on a config option.

DES
--
Dag-Erling Smørgrav - des@xxxxxx
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