Re: [dpdk-dev] [PATCH v13 2/5] eal: add the APIs to wait until equal

[Thomas Monjalon <thomas@monjalon.net>]

08/11/2019 17:38, Ananyev, Konstantin:
> > From: Gavin Hu <gavin.hu@arm.com>
> > +static __rte_always_inline void
> > +rte_wait_until_equal_64(volatile uint64_t *addr, uint64_t expected,
> > +		int memorder)
> > +{
> > +	uint64_t value;
> > +
> > +	assert(memorder == __ATOMIC_ACQUIRE || memorder == __ATOMIC_RELAXED);
> > +
> > +	/*
> > +	 * Atomic exclusive load from addr, it returns the 64-bit content of
> > +	 * *addr while making it 'monitored',when it is written by someone
> > +	 * else, the 'monitored' state is cleared and a event is generated
> > +	 * implicitly to exit WFE.
> > +	 */
> > +#define __LOAD_EXC_64(src, dst, memorder) {              \
> > +	if (memorder == __ATOMIC_RELAXED) {              \
> > +		asm volatile("ldxr %x[tmp], [%x[addr]]"  \
> > +			: [tmp] "=&r" (dst)              \
> > +			: [addr] "r"(src)                \
> > +			: "memory");                     \
> > +	} else {                                         \
> > +		asm volatile("ldaxr %x[tmp], [%x[addr]]" \
> > +			: [tmp] "=&r" (dst)              \
> > +			: [addr] "r"(src)                \
> > +			: "memory");                     \
> > +	} }
> > +
> > +	__LOAD_EXC_64(addr, value, memorder)
> > +	if (value != expected) {
> > +		__SEVL()
> > +		do {
> > +			__WFE()
> > +			__LOAD_EXC_64(addr, value, memorder)
> > +		} while (value != expected);
> > +	}
> > +}
> > +#undef __LOAD_EXC_64
> > +
> > +#undef __SEVL
> > +#undef __WFE
> 
> Personally I don't see how these define/undef are better then inline functions...

The benefit it to not pollute the API namespace
with some functions which are used only locally.
After using a macro, it disappears with #undef.

> Again I suppose they might be re-used in future some other ARM specific low-level primitvies.

Do this low-level routines _LOAD_EXC_ need to be exposed in EAL for re-use?

> My preference would be to keep them as inline function - much cleaner code.
> But as I don't develop for/use, I wouldn't insist and let you and arm guys to decide.