Re: [dpdk-dev] [PATCH v4 1/1] eal: add 128-bit compare exchange (x86-64 only)

["Eads, Gage" <gage.eads@intel.com>]

> 03/04/2019 19:34, Gage Eads:
> > This operation can be used for non-blocking algorithms, such as a
> > non-blocking stack or ring.
> >
> > Signed-off-by: Gage Eads <gage.eads@intel.com>
> > Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> > ---
> > --- a/lib/librte_eal/common/include/arch/x86/rte_atomic_64.h
> > +++ b/lib/librte_eal/common/include/arch/x86/rte_atomic_64.h
> > +/**
> > + * An atomic compare and set function used by the mutex functions.
> > + * (Atomically) Equivalent to:
> > + *   if (*dst == *exp)
> > + *     *dst = *src
> > + *   else
> > + *     *exp = *dst
> > + *
> > + * @note The success and failure arguments must be one of the
> > +__ATOMIC_* values
> > + * defined in the C++11 standard. For details on their behavior,
> > +refer to the
> > + * standard.
> > + *
> > + * @param dst
> > + *   The destination into which the value will be written.
> > + * @param exp
> > + *   Pointer to the expected value. If the operation fails, this memory is
> > + *   updated with the actual value.
> > + * @param src
> > + *   Pointer to the new value.
> > + * @param weak
> > + *   A value of true allows the comparison to spuriously fail and allows the
> > + *   'exp' update to occur non-atomically (i.e. a torn read may occur).
> > + *   Implementations may ignore this argument and only implement the
> strong
> > + *   variant.
> > + * @param success
> > + *   If successful, the operation's memory behavior conforms to this (or a
> > + *   stronger) model.
> > + * @param failure
> > + *   If unsuccessful, the operation's memory behavior conforms to this (or
> a
> > + *   stronger) model. This argument cannot be __ATOMIC_RELEASE,
> > + *   __ATOMIC_ACQ_REL, or a stronger model than success.
> > + * @return
> > + *   Non-zero on success; 0 on failure.
> > + */
> > +static inline int __rte_experimental
> > +rte_atomic128_cmp_exchange(rte_int128_t *dst,
> > +			   rte_int128_t *exp,
> > +			   const rte_int128_t *src,
> > +			   unsigned int weak,
> > +			   int success,
> > +			   int failure)
> 
> I was thinking about keeping the doxygen in the generic file.
> Is it possible?
> 

We'd need to include the definition of rte_int128_t, so we'd also need either an ifdef on RTE_ARCH_64 or RTE_ARCH_X86_64 to protect 32-bit builds. That macro would prevent doxygen from parsing that section, unless we add a workaround like, for example:

#if defined(RTE_ARCH_64) || defined(__DOXYGEN__)

So the patch would look like the v3, with the declaration in generic/rte_atomic.h, but with that preprocessor change. If we change RTE_ARCH_X86_64 to RTE_ARCH_64, I'd add a note clarifying that it's only implemented for x86-64. What do you think?