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

[Jerin Jacob <jerinjacobk@gmail.com>]

On Sat, Nov 9, 2019 at 12:07 AM Ananyev, Konstantin
<konstantin.ananyev@intel.com> wrote:
>
>
>
> > -----Original Message-----
> > From: Thomas Monjalon <thomas@monjalon.net>
> > Sent: Friday, November 8, 2019 5:00 PM
> > To: Ananyev, Konstantin <konstantin.ananyev@intel.com>
> > Cc: David Marchand <david.marchand@redhat.com>; dev@dpdk.org; nd@arm.com; Gavin Hu <gavin.hu@arm.com>; Mcnamara, John
> > <john.mcnamara@intel.com>; Kovacevic, Marko <marko.kovacevic@intel.com>; Jerin Jacob <jerinj@marvell.com>; Jan Viktorin
> > <viktorin@rehivetech.com>
> > Subject: Re: [PATCH v13 2/5] eal: add the APIs to wait until equal
> >
> > 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?
>
> About load_exc don't know for sure...
> Though as I can see wfe/sevl are used here:
> http://patchwork.dpdk.org/patch/61779/
> Might be it is possible to reuse these functions/macros...
> But again, I am not arm expert, would be interested to know what arm guys think.


Considering WFE has a requirement on using load_exec on ARM so IMO, it
makes sense to expose
load_exec in conjunction with wfe/sevl to use it properly.



>
> >
> > > 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.
> >
> >
>