Re: [dpdk-dev] [PATCH v4 1/5] eal: add new definitions for wait scheme

[Jerin Jacob <jerinjacobk@gmail.com>]

On Mon, Oct 25, 2021 at 3:01 PM Feifei Wang <Feifei.Wang2@arm.com> wrote:
>
> > -----邮件原件-----
> > 发件人: Jerin Jacob <jerinjacobk@gmail.com>
> > 发送时间: Friday, October 22, 2021 8:10 AM
> > 收件人: Feifei Wang <Feifei.Wang2@arm.com>
> > 抄送: Ruifeng Wang <Ruifeng.Wang@arm.com>; Ananyev, Konstantin
> > <konstantin.ananyev@intel.com>; dpdk-dev <dev@dpdk.org>; nd
> > <nd@arm.com>
> > 主题: Re: [dpdk-dev] [PATCH v4 1/5] eal: add new definitions for wait scheme
> >
> > On Wed, Oct 20, 2021 at 2:16 PM Feifei Wang <feifei.wang2@arm.com>
> > wrote:
> > >
> > > Introduce macros as generic interface for address monitoring.
> > >
> > > Signed-off-by: Feifei Wang <feifei.wang2@arm.com>
> > > Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
> > > ---
> > >  lib/eal/arm/include/rte_pause_64.h  | 126
> > > ++++++++++++++++------------  lib/eal/include/generic/rte_pause.h |
> > > 32 +++++++
> > >  2 files changed, 104 insertions(+), 54 deletions(-)
> > >
> > > diff --git a/lib/eal/arm/include/rte_pause_64.h
> > > b/lib/eal/arm/include/rte_pause_64.h
> > > index e87d10b8cc..23954c2de2 100644
> > > --- a/lib/eal/arm/include/rte_pause_64.h
> > > +++ b/lib/eal/arm/include/rte_pause_64.h
> > > @@ -31,20 +31,12 @@ static inline void rte_pause(void)
> > >  /* Put processor into low power WFE(Wait For Event) state. */
> > > #define __WFE() { asm volatile("wfe" : : : "memory"); }
> > >
> > > -static __rte_always_inline void
> > > -rte_wait_until_equal_16(volatile uint16_t *addr, uint16_t expected,
> > > -               int memorder)
> > > -{
> > > -       uint16_t value;
> > > -
> > > -       assert(memorder == __ATOMIC_ACQUIRE || memorder ==
> > __ATOMIC_RELAXED);
> > > -
> > > -       /*
> > > -        * Atomic exclusive load from addr, it returns the 16-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
> >
> > a event -> an event in all the occurrence.
> >
> > > -        * implicitly to exit WFE.
> > > -        */
> > > +/*
> > > + * Atomic exclusive load from addr, it returns the 16-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_16(src, dst, memorder) {               \
> > >         if (memorder == __ATOMIC_RELAXED) {               \
> > >                 asm volatile("ldxrh %w[tmp], [%x[addr]]"  \ @@ -58,6
> > > +50,52 @@ rte_wait_until_equal_16(volatile uint16_t *addr, uint16_t
> > expected,
> > >                         : "memory");                      \
> > >         } }
> > >
> > > +/*
> > > + * Atomic exclusive load from addr, it returns the 32-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_32(src, dst, memorder) {              \
> > > +       if (memorder == __ATOMIC_RELAXED) {              \
> > > +               asm volatile("ldxr %w[tmp], [%x[addr]]"  \
> > > +                       : [tmp] "=&r" (dst)              \
> > > +                       : [addr] "r"(src)                \
> > > +                       : "memory");                     \
> > > +       } else {                                         \
> > > +               asm volatile("ldaxr %w[tmp], [%x[addr]]" \
> > > +                       : [tmp] "=&r" (dst)              \
> > > +                       : [addr] "r"(src)                \
> > > +                       : "memory");                     \
> > > +       } }
> > > +
> > > +/*
> > > + * 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");                     \
> > > +       } }
> > > +
> > > +static __rte_always_inline void
> > > +rte_wait_until_equal_16(volatile uint16_t *addr, uint16_t expected,
> > > +               int memorder)
> > > +{
> > > +       uint16_t value;
> > > +
> > > +       assert(memorder == __ATOMIC_ACQUIRE || memorder ==
> > > + __ATOMIC_RELAXED);
> > > +
> > >         __LOAD_EXC_16(addr, value, memorder)
> > >         if (value != expected) {
> > >                 __SEVL()
> > > @@ -66,7 +104,6 @@ rte_wait_until_equal_16(volatile uint16_t *addr,
> > uint16_t expected,
> > >                         __LOAD_EXC_16(addr, value, memorder)
> > >                 } while (value != expected);
> > >         }
> > > -#undef __LOAD_EXC_16
> > >  }
> > >
> > >  static __rte_always_inline void
> > > @@ -77,25 +114,6 @@ rte_wait_until_equal_32(volatile uint32_t *addr,
> > > uint32_t expected,
> > >
> > >         assert(memorder == __ATOMIC_ACQUIRE || memorder ==
> > > __ATOMIC_RELAXED);
> > >
> > > -       /*
> > > -        * Atomic exclusive load from addr, it returns the 32-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_32(src, dst, memorder) {              \
> > > -       if (memorder == __ATOMIC_RELAXED) {              \
> > > -               asm volatile("ldxr %w[tmp], [%x[addr]]"  \
> > > -                       : [tmp] "=&r" (dst)              \
> > > -                       : [addr] "r"(src)                \
> > > -                       : "memory");                     \
> > > -       } else {                                         \
> > > -               asm volatile("ldaxr %w[tmp], [%x[addr]]" \
> > > -                       : [tmp] "=&r" (dst)              \
> > > -                       : [addr] "r"(src)                \
> > > -                       : "memory");                     \
> > > -       } }
> > > -
> > >         __LOAD_EXC_32(addr, value, memorder)
> > >         if (value != expected) {
> > >                 __SEVL()
> > > @@ -104,7 +122,6 @@ rte_wait_until_equal_32(volatile uint32_t *addr,
> > uint32_t expected,
> > >                         __LOAD_EXC_32(addr, value, memorder)
> > >                 } while (value != expected);
> > >         }
> > > -#undef __LOAD_EXC_32
> > >  }
> > >
> > >  static __rte_always_inline void
> > > @@ -115,25 +132,6 @@ rte_wait_until_equal_64(volatile uint64_t *addr,
> > > uint64_t expected,
> > >
> > >         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()
> > > @@ -143,6 +141,26 @@ rte_wait_until_equal_64(volatile uint64_t *addr,
> > uint64_t expected,
> > >                 } while (value != expected);
> > >         }
> > >  }
> > > +
> > > +#define rte_wait_event(addr, mask, expected, cond, memorder, size) \
> >
> > I think it is better to swap "cond" and "expected" positions to get better
> > readability.
> Thanks for the comments, it is better than before and I will update in the next version.
> >
> >  rte_wait_event(&buf->bufptr64, RTE_DISTRIB_FLAGS_MASK, 0, !=,
> > __ATOMIC_RELAXED, 64);
> >
> > Vs
> >
> >  rte_wait_event(&buf->bufptr64, RTE_DISTRIB_FLAGS_MASK, !=, 0,
> > __ATOMIC_RELAXED, 64);
> >
> > > +do {                                                               \
> >
> > Any reason to not make an inline function instead of macro?
> Because there were many new APIs for different cases. And then we refer to
> Linux 'wait_event' code for an example. Please see the first version and its discussion:
> http://patches.dpdk.org/project/dpdk/cover/20210902053253.3017858-1-feifei.wang2@arm.com/


OK.


> >
> > > +       RTE_BUILD_BUG_ON(!__builtin_constant_p(memorder));         \
> >
> > Should n't we add __builtin_constant_p(size) of check?
>
> Please see the discussion with Konstantin.
> 'size' will not be as a parameter and then it is unnecessary to check it with build_bug.

Make sense to remove the 'size'. My comment was more in the direction
of, if the 'size' is required to pass.

> >
> > > +       RTE_BUILD_BUG_ON(memorder != __ATOMIC_ACQUIRE &&           \
> > > +       memorder != __ATOMIC_RELAXED);                             \
> > > +       RTE_BUILD_BUG_ON(size != 16 && size != 32 && size != 64);  \
> > > +       uint##size_t value;
> >
> >
> >                                \
> > > +       __LOAD_EXC_##size(addr, value, memorder)                   \
> > > +       if ((value & mask) cond expected) {                        \
> > > +               __SEVL()                                           \
> > > +               do {                                               \
> > > +                       __WFE()                                    \
> > > +                       __LOAD_EXC_##size(addr, value, memorder)   \
> > > +               } while ((value & mask) cond expected);            \
> > > +       }                                                          \
> > > +} while (0)
> > > +
> > > +#undef __LOAD_EXC_16
> > > +#undef __LOAD_EXC_32
> > >  #undef __LOAD_EXC_64
> > >
> > >  #undef __SEVL
> > > diff --git a/lib/eal/include/generic/rte_pause.h
> > > b/lib/eal/include/generic/rte_pause.h
> > > index 668ee4a184..20a5d2a9fd 100644
> > > --- a/lib/eal/include/generic/rte_pause.h
> > > +++ b/lib/eal/include/generic/rte_pause.h
> > > @@ -111,6 +111,38 @@ rte_wait_until_equal_64(volatile uint64_t *addr,
> > uint64_t expected,
> > >         while (__atomic_load_n(addr, memorder) != expected)
> > >                 rte_pause();
> > >  }
> > > +
> > > +/*
> > > + * Wait until *addr breaks the condition, with a relaxed memory
> > > + * ordering model meaning the loads around this API can be reordered.
> > > + *
> > > + * @param addr
> > > + *  A pointer to the memory location.
> > > + * @param mask
> > > + *  A mask of value bits in interest.
> > > + * @param expected
> > > + *  A 16-bit expected value to be in the memory location.
> > > + * @param cond
> > > + *  A symbol representing the condition (==, !=).
> > > + * @param memorder
> > > + *  Two different memory orders that can be specified:
> > > + *  __ATOMIC_ACQUIRE and __ATOMIC_RELAXED. These map to
> > > + *  C++11 memory orders with the same names, see the C++11 standard
> > > +or
> > > + *  the GCC wiki on atomic synchronization for detailed definition.
> > > + * @param size
> > > + * The bit size of *addr:
> > > + * It is used for arm architecture to choose load instructions,
> > > + * and the optional value is 16, 32 and 64.
> > > + */
> > > +#define rte_wait_event(addr, mask, expected, cond, memorder, size)     \
> > > +do {                                                                   \
> > > +       RTE_BUILD_BUG_ON(!__builtin_constant_p(memorder));             \
> > > +       RTE_BUILD_BUG_ON(memorder != __ATOMIC_ACQUIRE &&               \
> > > +                               memorder != __ATOMIC_RELAXED);         \
> > > +       RTE_BUILD_BUG_ON(size != 16 && size != 32 && size != 64);      \
> > > +       while ((__atomic_load_n(addr, memorder) & mask) cond expected) \
> > > +               rte_pause();                                           \
> > > +} while (0)
> > >  #endif
> > >
> > >  #endif /* _RTE_PAUSE_H_ */
> > > --
> > > 2.25.1
> > >