Re: [dpdk-dev] [PATCH v1 1/5] lib/eal: implement the family of rte bitoperation APIs

["Morten Brørup" <mb@smartsharesystems.com>]

> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Joyce Kong
> Sent: Tuesday, October 15, 2019 9:50 AM
> 
> There are a lot functions of bit operations scattered and
> duplicated in PMDs, consolidating them into a common API
> family is necessary. Furthermore, the bit operation is
> mostly applied to the IO devices, so use __ATOMIC_ACQ_REL
> to ensure the ordering.

Good initiative.

> 
> Signed-off-by: Joyce Kong <joyce.kong@arm.com>
> ---
>  lib/librte_eal/common/Makefile             |  1 +
>  lib/librte_eal/common/include/rte_bitops.h | 56
> ++++++++++++++++++++++++++++++
>  lib/librte_eal/common/meson.build          |  1 +
>  3 files changed, 58 insertions(+)
>  create mode 100644 lib/librte_eal/common/include/rte_bitops.h
> 
> diff --git a/lib/librte_eal/common/Makefile
> b/lib/librte_eal/common/Makefile
> index a00d4fc..8586ca8 100644
> --- a/lib/librte_eal/common/Makefile
> +++ b/lib/librte_eal/common/Makefile
> @@ -18,6 +18,7 @@ INC += rte_malloc.h rte_keepalive.h rte_time.h
>  INC += rte_service.h rte_service_component.h
>  INC += rte_bitmap.h rte_vfio.h rte_hypervisor.h rte_test.h
>  INC += rte_reciprocal.h rte_fbarray.h rte_uuid.h
> +INC += rte_bitops.h
> 
>  GENERIC_INC := rte_atomic.h rte_byteorder.h rte_cycles.h
> rte_prefetch.h
>  GENERIC_INC += rte_memcpy.h rte_cpuflags.h
> diff --git a/lib/librte_eal/common/include/rte_bitops.h
> b/lib/librte_eal/common/include/rte_bitops.h
> new file mode 100644
> index 0000000..4d7c5a3
> --- /dev/null
> +++ b/lib/librte_eal/common/include/rte_bitops.h
> @@ -0,0 +1,56 @@
> +/* SPDX-License-Identifier: BSD-3-Clause
> + * Copyright(c) 2019 Arm Corporation
> + */
> +
> +#ifndef _RTE_BITOPS_H_
> +#define _RTE_BITOPS_H_
> +
> +/**
> + * @file
> + * Bit Operations
> + *
> + * This file defines a generic API for bit operations.
> + */
> +
> +#include <stdint.h>
> +#include <rte_atomic.h>
> +
> +static inline void
> +rte_set_bit(unsigned int nr, unsigned long *addr)
> +{
> +	__atomic_fetch_or(addr, (1UL << nr), __ATOMIC_ACQ_REL);
> +}
> +
> +static inline void
> +rte_clear_bit(int nr, unsigned long *addr)
> +{
> +	__atomic_fetch_and(addr, ~(1UL << nr), __ATOMIC_ACQ_REL);
> +}
> +
> +static inline int
> +rte_test_bit(int nr, unsigned long *addr)
> +{
> +	int res;
> +	rte_mb();
> +	res = ((*addr) & (1UL << nr)) != 0;
> +	rte_mb();
> +
> +	return res;
> +}

Why does rte_test_bit() not use any of the __atomic_xx functions instead? E.g.:

static inline int
rte_test_bit(int nr, unsigned long *addr)
{
	return __atomic_load_n(addr, __ATOMIC_ACQUIRE);
}

> +
> +static inline int
> +rte_test_and_set_bit(int nr, unsigned long *addr)
> +{
> +	unsigned long mask = (1UL << nr);
> +
> +	return __atomic_fetch_or(addr, mask, __ATOMIC_ACQ_REL) & mask;
> +}
> +
> +static inline int
> +rte_test_and_clear_bit(int nr, unsigned long *addr)
> +{
> +	unsigned long mask = (1UL << nr);
> +
> +	return __atomic_fetch_and(addr, ~mask, __ATOMIC_ACQ_REL) & mask;
> +}
> +#endif /* _RTE_BITOPS_H_ */
> diff --git a/lib/librte_eal/common/meson.build
> b/lib/librte_eal/common/meson.build
> index 386577c..a277cdf 100644
> --- a/lib/librte_eal/common/meson.build
> +++ b/lib/librte_eal/common/meson.build
> @@ -52,6 +52,7 @@ common_headers = files(
>  	'include/rte_alarm.h',
>  	'include/rte_branch_prediction.h',
>  	'include/rte_bus.h',
> +	'include/rte_bitops.h',
>  	'include/rte_bitmap.h',
>  	'include/rte_class.h',
>  	'include/rte_common.h',
> --
> 2.7.4
> 

These functions use unsigned long as the type of their value, like they do in the PMDs.

However, a generic bit operations library should preferably work with multiple types, like the __atomic_xx functions. Or use an well defined uint_NN_t type. Or have individually named functions for each type size, e.g. rte_set_bit_32() and rte_set_bit_64().


Med venlig hilsen / kind regards
- Morten Brørup