[dpdk-dev] [PATCH v7 2/7] eal: add the APIs to wait until equal

[Ananyev, Konstantin]

> 
> Hi Gavin,
> 
> >
> > The rte_wait_until_equal_xx APIs abstract the functionality of
> > 'polling for a memory location to become equal to a given value'.
> >
> > Add the RTE_ARM_USE_WFE configuration entry for aarch64, disabled
> > by default. When it is enabled, the above APIs will call WFE instruction
> > to save CPU cycles and power.
> >
> > Signed-off-by: Gavin Hu <gavin.hu at arm.com>
> > Reviewed-by: Ruifeng Wang <ruifeng.wang at arm.com>
> > Reviewed-by: Steve Capper <steve.capper at arm.com>
> > Reviewed-by: Ola Liljedahl <ola.liljedahl at arm.com>
> > Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli at arm.com>
> > Reviewed-by: Phil Yang <phil.yang at arm.com>
> > Acked-by: Pavan Nikhilesh <pbhagavatula at marvell.com>
> > ---
> >  config/arm/meson.build                             |   1 +
> >  config/common_base                                 |   5 +
> >  .../common/include/arch/arm/rte_pause_64.h         |  30 ++++++
> >  lib/librte_eal/common/include/generic/rte_pause.h  | 106 +++++++++++++++++++++
> >  4 files changed, 142 insertions(+)
> >
> > diff --git a/config/arm/meson.build b/config/arm/meson.build
> > index 979018e..b4b4cac 100644
> > --- a/config/arm/meson.build
> > +++ b/config/arm/meson.build
> > @@ -26,6 +26,7 @@ flags_common_default = [
> >  	['RTE_LIBRTE_AVP_PMD', false],
> >
> >  	['RTE_SCHED_VECTOR', false],
> > +	['RTE_ARM_USE_WFE', false],
> >  ]
> >
> >  flags_generic = [
> > diff --git a/config/common_base b/config/common_base
> > index 8ef75c2..8861713 100644
> > --- a/config/common_base
> > +++ b/config/common_base
> > @@ -111,6 +111,11 @@ CONFIG_RTE_MAX_VFIO_CONTAINERS=64
> >  CONFIG_RTE_MALLOC_DEBUG=n
> >  CONFIG_RTE_EAL_NUMA_AWARE_HUGEPAGES=n
> >  CONFIG_RTE_USE_LIBBSD=n
> > +# Use WFE instructions to implement the rte_wait_for_equal_xxx APIs,
> > +# calling these APIs put the cores in low power state while waiting
> > +# for the memory address to become equal to the expected value.
> > +# This is supported only by aarch64.
> > +CONFIG_RTE_ARM_USE_WFE=n
> >
> >  #
> >  # Recognize/ignore the AVX/AVX512 CPU flags for performance/power testing.
> > 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"); \
> > +}

One more thought:
Why do you need to write asm code for the whole procedure?
Why not to do like linux kernel:
define wfe() and sev() macros and use them inside normal C code?
 
#define sev()		asm volatile("sev" : : : "memory")
#define wfe()		asm volatile("wfe" : : : "memory")

Then:
rte_wait_until_equal_32(volatile uint32_t *addr, uint32_t expected, int memorder)
{
     if (__atomic_load_n(addr, memorder) != expected) {
         sev();
         do {
             wfe();
         } while ((__atomic_load_n(addr, memorder) != expected);
     }
}

?

> > +/* 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
> > +
> >  #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..8906473 100644
> > --- a/lib/librte_eal/common/include/generic/rte_pause.h
> > +++ b/lib/librte_eal/common/include/generic/rte_pause.h
> > @@ -1,5 +1,6 @@
> >  /* SPDX-License-Identifier: BSD-3-Clause
> >   * Copyright(c) 2017 Cavium, Inc
> > + * Copyright(c) 2019 Arm Limited
> >   */
> >
> >  #ifndef _RTE_PAUSE_H_
> > @@ -12,6 +13,10 @@
> >   *
> >   */
> >
> > +#include <stdint.h>
> > +#include <rte_common.h>
> > +#include <rte_atomic.h>
> > +
> >  /**
> >   * Pause CPU execution for a short while
> >   *
> > @@ -20,4 +25,105 @@
> >   */
> >  static inline void rte_pause(void);
> >
> > +/**
> > + * Wait for *addr to be updated with a 16-bit expected value, with a relaxed
> > + * memory ordering model meaning the loads around this API can be reordered.
> > + *
> > + * @param addr
> > + *  A pointer to the memory location.
> > + * @param expected
> > + *  A 16-bit 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 a 32-bit expected value, with a relaxed
> > + * memory ordering model meaning the loads around this API can be reordered.
> > + *
> > + * @param addr
> > + *  A pointer to the memory location.
> > + * @param expected
> > + *  A 32-bit expected value to be in the memory location.
> > + */
> > +__rte_always_inline
> > +static void
> > +rte_wait_until_equal_relaxed_32(volatile uint32_t *addr, uint32_t expected);
> > +
> > +/**
> > + * Wait for *addr to be updated with a 64-bit expected value, with a relaxed
> > + * memory ordering model meaning the loads around this API can be reordered.
> > + *
> > + * @param addr
> > + *  A pointer to the memory location.
> > + * @param expected
> > + *  A 64-bit expected value to be in the memory location.
> > + */
> > +__rte_always_inline
> > +static void
> > +rte_wait_until_equal_relaxed_64(volatile uint64_t *addr, uint64_t expected);
> > +
> > +/**
> > + * Wait for *addr to be updated with a 16-bit expected value, with an acquire
> > + * memory ordering model meaning the loads after this API can't be observed
> > + * before this API.
> > + *
> > + * @param addr
> > + *  A pointer to the memory location.
> > + * @param expected
> > + *  A 16-bit expected value to be in the memory location.
> > + */
> > +__rte_always_inline
> > +static void
> > +rte_wait_until_equal_acquire_16(volatile uint16_t *addr, uint16_t expected);
> > +
> > +/**
> > + * Wait for *addr to be updated with a 32-bit expected value, with an acquire
> > + * memory ordering model meaning the loads after this API can't be observed
> > + * before this API.
> > + *
> > + * @param addr
> > + *  A pointer to the memory location.
> > + * @param expected
> > + *  A 32-bit expected value to be in the memory location.
> > + */
> > +__rte_always_inline
> > +static void
> > +rte_wait_until_equal_acquire_32(volatile uint32_t *addr, uint32_t expected);
> 
> LGTM in general.
> One stylish thing: wouldn't it be better to have an API like that:
> rte_wait_until_equal_acquire_X(addr, expected, memory_order)
> ?
> 
> I.E. - pass memorder as parameter, not to incorporate it into function name?
> Less functions, plus user can specify order himself.
> Plus looks similar to C11 atomic instrincts.
> 
> 
> > +
> > +/**
> > + * Wait for *addr to be updated with a 64-bit expected value, with an acquire
> > + * memory ordering model meaning the loads after this API can't be observed
> > + * before this API.
> > + *
> > + * @param addr
> > + *  A pointer to the memory location.
> > + * @param expected
> > + *  A 64-bit 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)
> > +#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