Hi Konstantin,
> -----Original Message-----
> From: Ananyev, Konstantin <konstantin.anan...@intel.com>
> Sent: Friday, October 18, 2019 12:44 AM
> To: Gavin Hu (Arm Technology China) <gavin...@arm.com>;
> dev@dpdk.org
> Cc: nd <n...@arm.com>; tho...@monjalon.net;
> step...@networkplumber.org; hemant.agra...@nxp.com;
> jer...@marvell.com; pbhagavat...@marvell.com; Honnappa Nagarahalli
> <honnappa.nagaraha...@arm.com>; Ruifeng Wang (Arm Technology China)
> <ruifeng.w...@arm.com>; Phil Yang (Arm Technology China)
> <phil.y...@arm.com>; Steve Capper <steve.cap...@arm.com>
> Subject: RE: [dpdk-dev] [PATCH v7 2/7] eal: add the APIs to wait until equal
>
>
> >
> > 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...@arm.com>
> > > Reviewed-by: Ruifeng Wang <ruifeng.w...@arm.com>
> > > Reviewed-by: Steve Capper <steve.cap...@arm.com>
> > > Reviewed-by: Ola Liljedahl <ola.liljed...@arm.com>
> > > Reviewed-by: Honnappa Nagarahalli <honnappa.nagaraha...@arm.com>
> > > Reviewed-by: Phil Yang <phil.y...@arm.com>
> > > Acked-by: Pavan Nikhilesh <pbhagavat...@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);
> }
> }
>
> ?
A really good suggestion, I made corresponding changes to v8 already, but it
missed a armv8 specific feature after internal discussion.
We call wfe to wait/sleep on the 'monitored' address, it will be waken up upon
someone write to the monitor address, so before wfe, we have to call
load-exclusive instruction to 'monitor'.
__atomic_load_n - disassembled to "ldr" does not do so. We have to use "ldxrh"
for relaxed mem ordering and "ldaxrh" for acquire ordering, in example of
16-bit.
Let me re-think coming back to the full assembly procedure or implementing a
'load-exclusive' function. What do you think?
/Gavin
> > > +/* 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
