Re: [dpdk-dev] [PATCH v5 3/8] eal: add the APIs to wait until equal

["Gavin Hu (Arm Technology China)" <Gavin.Hu@arm.com>]

Hi Jerin,

> -----Original Message-----
> From: Jerin Jacob <jerinjacobk@gmail.com>
> Sent: Friday, September 13, 2019 12:12 AM
> To: Gavin Hu (Arm Technology China) <Gavin.Hu@arm.com>
> Cc: dev@dpdk.org; nd <nd@arm.com>; thomas@monjalon.net;
> stephen@networkplumber.org; hemant.agrawal@nxp.com;
> jerinj@marvell.com; Pavan Nikhilesh <pbhagavatula@marvell.com>;
> Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
> Subject: Re: [dpdk-dev] [PATCH v5 3/8] eal: add the APIs to wait until equal
> 
> On Thu, Sep 12, 2019 at 4:56 PM Gavin Hu <gavin.hu@arm.com> wrote:
> >
> > The rte_wait_until_equalxx APIs abstract the functionality of 'polling
> > for a memory location to become equal to a given value'.
> >
> > Signed-off-by: Gavin Hu <gavin.hu@arm.com>
> > Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
> > Reviewed-by: Steve Capper <steve.capper@arm.com>
> > Reviewed-by: Ola Liljedahl <ola.liljedahl@arm.com>
> > Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> > Reviewed-by: Phil Yang <phil.yang@arm.com>
> > Acked-by: Pavan Nikhilesh <pbhagavatula@marvell.com>
> > ---
> >  .../common/include/arch/arm/rte_pause_64.h         | 30 +++++++
> >  lib/librte_eal/common/include/generic/rte_pause.h  | 98
> +++++++++++++++++++++-
> >  2 files changed, 127 insertions(+), 1 deletion(-)
> >
> > diff --git a/lib/librte_eal/common/include/arch/arm/rte_pause_64.h
> b/lib/librte_eal/common/include/arch/arm/rte_pause_64.h
> > index 93895d3..dabde17 100644
> > --- a/lib/librte_eal/common/include/arch/arm/rte_pause_64.h
> > +++ b/lib/librte_eal/common/include/arch/arm/rte_pause_64.h
> > @@ -1,5 +1,6 @@
> >  /* SPDX-License-Identifier: BSD-3-Clause
> >   * Copyright(c) 2017 Cavium, Inc
> > + * Copyright(c) 2019 Arm Limited
> >   */
> >
> >  #ifndef _RTE_PAUSE_ARM64_H_
> > @@ -17,6 +18,35 @@ static inline void rte_pause(void)
> >         asm volatile("yield" ::: "memory");
> >  }
> >
> > +#ifdef RTE_ARM_USE_WFE
> > +#define __WAIT_UNTIL_EQUAL(name, asm_op, wide, type) \
> > +static __rte_always_inline void \
> > +rte_wait_until_equal_##name(volatile type * addr, type expected) \
> > +{ \
> > +       type tmp; \
> > +       asm volatile( \
> > +               #asm_op " %" #wide "[tmp], %[addr]\n" \
> > +               "cmp    %" #wide "[tmp], %" #wide "[expected]\n" \
> > +               "b.eq   2f\n" \
> > +               "sevl\n" \
> > +               "1:     wfe\n" \
> > +               #asm_op " %" #wide "[tmp], %[addr]\n" \
> > +               "cmp    %" #wide "[tmp], %" #wide "[expected]\n" \
> > +               "bne    1b\n" \
> > +               "2:\n" \
> > +               : [tmp] "=&r" (tmp) \
> > +               : [addr] "Q"(*addr), [expected] "r"(expected) \
> > +               : "cc", "memory"); \
> > +}
> > +/* Wait for *addr to be updated with expected value */
> > +__WAIT_UNTIL_EQUAL(relaxed_16, ldxrh, w, uint16_t)
> > +__WAIT_UNTIL_EQUAL(acquire_16, ldaxrh, w, uint16_t)
> > +__WAIT_UNTIL_EQUAL(relaxed_32, ldxr, w, uint32_t)
> > +__WAIT_UNTIL_EQUAL(acquire_32, ldaxr, w, uint32_t)
> > +__WAIT_UNTIL_EQUAL(relaxed_64, ldxr, x, uint64_t)
> > +__WAIT_UNTIL_EQUAL(acquire_64, ldaxr, x, uint64_t)
> > +#endif
> 
> Looks good.
> 
> > +
> >  #ifdef __cplusplus
> >  }
> >  #endif
> > diff --git a/lib/librte_eal/common/include/generic/rte_pause.h
> b/lib/librte_eal/common/include/generic/rte_pause.h
> > index 52bd4db..dfa6a53 100644
> > --- a/lib/librte_eal/common/include/generic/rte_pause.h
> > +++ b/lib/librte_eal/common/include/generic/rte_pause.h
> > @@ -1,10 +1,10 @@
> >  /* SPDX-License-Identifier: BSD-3-Clause
> >   * Copyright(c) 2017 Cavium, Inc
> > + * Copyright(c) 2019 Arm Limited
> >   */
> >
> >  #ifndef _RTE_PAUSE_H_
> >  #define _RTE_PAUSE_H_
> > -
> 
> Unwanted change.
Will fix it.
> 
> >  /**
> >   * @file
> >   *
> > @@ -12,6 +12,10 @@
> >   *
> >   */
> >
> > +#include <stdint.h>
> > +#include <rte_common.h>
> > +#include <rte_atomic.h>
> > +
> >  /**
> >   * Pause CPU execution for a short while
> >   *
> > @@ -20,4 +24,96 @@
> >   */
> >  static inline void rte_pause(void);
> >
> > +/**
> > + * Wait for *addr to be updated with expected value
> 
> IMO, We need to mention relaxed attribute also in the comment.
Will fix it.
> 
> > + *
> > + * @param addr
> > + *  A pointer to the memory location.
> > + * @param expected
> > + *  An expected value to be in the memory location.
> > + */
> > +__rte_always_inline
> > +static void
> > +rte_wait_until_equal_relaxed_16(volatile uint16_t *addr, uint16_t
> expected);
> 
> > +
> > +/**
> > + * Wait for *addr to be updated with expected value
> > + *
> > + * @param addr
> > + *  A pointer to the memory location.
> > + * @param expected
> > + *  An expected value to be in the memory location.
> > + */
> > +__rte_always_inline
> > +static void
> > +rte_wait_until_equal_acquire_64(volatile uint64_t *addr, uint64_t
> expected);
> > +
> > +#if !defined(RTE_ARM_USE_WFE)
> 
> Looks like there is a side effect as meson's build/rte_build_config.h
> comes as below
> #define RTE_ARM_USE_WFE 0
> 
> So actually it is defined.
Good catch, thanks, will fix it.
> 
> > +#define __WAIT_UNTIL_EQUAL(op_name, size, type, memorder) \
> > +__rte_always_inline \
> > +static void    \
> > +rte_wait_until_equal_##op_name##_##size(volatile type *addr, \
> > +       type expected) \
> > +{ \
> > +       while (__atomic_load_n(addr, memorder) != expected) \
> > +               rte_pause(); \
> > +}
> > +
> > +/* Wait for *addr to be updated with expected value */
> > +__WAIT_UNTIL_EQUAL(relaxed, 16, uint16_t, __ATOMIC_RELAXED)
> > +__WAIT_UNTIL_EQUAL(acquire, 16, uint16_t, __ATOMIC_ACQUIRE)
> > +__WAIT_UNTIL_EQUAL(relaxed, 32, uint32_t, __ATOMIC_RELAXED)
> > +__WAIT_UNTIL_EQUAL(acquire, 32, uint32_t, __ATOMIC_ACQUIRE)
> > +__WAIT_UNTIL_EQUAL(relaxed, 64, uint64_t, __ATOMIC_RELAXED)
> > +__WAIT_UNTIL_EQUAL(acquire, 64, uint64_t, __ATOMIC_ACQUIRE)
> > +#endif /* RTE_ARM_USE_WFE */
> > +
> >  #endif /* _RTE_PAUSE_H_ */
> > --
> > 2.7.4
> >