ZFS committed to the FreeBSD base.

Dag-Erling Smørgrav des at des.no
Thu Apr 12 08:54:23 UTC 2007

Peter Jeremy <peterjeremy at optushome.com.au> 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.

Dag-Erling Smørgrav - des at des.no

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