Re: [dpdk-dev] [PATCH v2 1/6] lib/eal: implement the family of rte bit operation APIs

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

> -----Original Message-----
> From: Joyce Kong [mailto:joyce.kong@arm.com]
> Sent: Wednesday, October 23, 2019 4:55 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.
> 
> Signed-off-by: Joyce Kong <joyce.kong@arm.com>
> Reviewed-by: Gavin Hu <gavin.hu@arm.com>
> ---
>  lib/librte_eal/common/Makefile                |   1 +
>  lib/librte_eal/common/include/rte_io_bitops.h | 112
> ++++++++++++++++++++++++++
>  lib/librte_eal/common/meson.build             |   1 +
>  3 files changed, 114 insertions(+)
>  create mode 100644 lib/librte_eal/common/include/rte_io_bitops.h
> 
> diff --git a/lib/librte_eal/common/Makefile
> b/lib/librte_eal/common/Makefile
> index a00d4fc..3831313 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_io_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_io_bitops.h
> b/lib/librte_eal/common/include/rte_io_bitops.h
> new file mode 100644
> index 0000000..5f778b8
> --- /dev/null
> +++ b/lib/librte_eal/common/include/rte_io_bitops.h
> @@ -0,0 +1,112 @@
> +/* SPDX-License-Identifier: BSD-3-Clause
> + * Copyright(c) 2019 Arm Limited
> + */
> +
> +#ifndef _RTE_IO_BITOPS_H_
> +#define _RTE_IO_BITOPS_H_
> +
> +/**
> + * @file
> + * Bit Operations
> + *
> + * This file defines a generic API for bit operations.
> + */

-> This file defines a generic API for I/O device bit operations.

> +
> +#include <rte_lcore.h>

This library doesn't do any lcore operations. Please use the appropriate headers.

> +
> +/**
> + * Get a bit.
> + *
> + * @param nr
> + *   The bit to get.
> + * @param addr
> + *   The address to count from.

The address to count from. -> The address holding the bit. (Applies to all functions.)

> + * @return
> + *   The value of the bit.

The description of the return value can be misinterpreted. The return value is not the value of the bit, which is 0 or 1, but the value of the word holding the bit, masked with the bit position. (Applies to all functions returning a value.)

> + */
> +static inline int32_t
> +rte_io_get_bit(uint32_t nr, uint64_t *addr)

The return type should be an unsigned type. (Applies to all functions returning a value.)

The addr type for 32 bit operations should not be uint64_t *, but uint32_t *. The __atomic_xxx functions actually use this type for something, and I think it would access the wrong 32 bits on a big endian CPU.

In some of the functions below, nr is signed (int32_t); it should be unsigned (uint32_t).

And a suggestion: Consider changing the type of nr from uint32_t to unsigned int.

> +{
> +	return __atomic_load_n(addr, __ATOMIC_ACQUIRE) & (1UL << nr);
> +}
> +
> +/**
> + * Set a bit to 1.
> + *
> + * @param nr
> + *   The bit to set.
> + * @param addr
> + *   The address to count from.
> + */
> +static inline void
> +rte_io_set_bit(uint32_t nr, uint64_t *addr)
> +{
> +	__atomic_fetch_or(addr, (1UL << nr), __ATOMIC_ACQ_REL);
> +}
> +
> +/**
> + * Set a bit to 0.
> + *
> + * @param nr
> + *   The bit to set.
> + * @param addr
> + *   The address to count from.
> + */
> +static inline void
> +rte_io_clear_bit(int32_t nr, uint64_t *addr)
> +{
> +	__atomic_fetch_and(addr, ~(1UL << nr), __ATOMIC_ACQ_REL);
> +}
> +
> +/**
> + * Test if a bit is 1.
> + *
> + * @param nr
> + *   The bit to test.
> + * @param addr
> + *   The address to count from.
> + * @return
> + *   1 if the bit is 1; else 0.
> + */
> +static inline int32_t
> +rte_io_test_bit(int32_t nr, uint64_t *addr)
> +{
> +	return (__atomic_load_n(addr, __ATOMIC_ACQUIRE) & (1UL << nr)) !=
> 0;
> +}

All the other functions in this library return a word with the bit masked. This function returns 0 or 1. I think it should return a word value, similar to the other functions.

> +
> +/**
> + * Set a bit to 1 and return its old value.
> + *
> + * @param nr
> + *   The bit to set.
> + * @param addr
> + *   The address to count from.
> + * @return
> + *   The old value of the bit.
> + */
> +static inline int32_t
> +rte_io_test_and_set_bit(int32_t nr, uint64_t *addr)
> +{
> +	unsigned long mask = (1UL << nr);

unsigned long mask -> uint32_t mask. (Also applies to other functions.)

> +
> +	return __atomic_fetch_or(addr, mask, __ATOMIC_ACQ_REL) & mask;
> +}
> +
> +/**
> + * Set a bit to 0 and return its old value.
> + *
> + * @param nr
> + *   The bit to set.
> + * @param addr
> + *   The address to count from.
> + * @return
> + *   The old value of the bit.
> + */
> +static inline int32_t
> +rte_io_test_and_clear_bit(int32_t nr, uint64_t *addr)
> +{
> +	unsigned long mask = (1UL << nr);
> +
> +	return __atomic_fetch_and(addr, ~mask, __ATOMIC_ACQ_REL) & mask;
> +}
> +#endif /* _RTE_IO_BITOPS_H_ */
> diff --git a/lib/librte_eal/common/meson.build
> b/lib/librte_eal/common/meson.build
> index 386577c..0a65d04 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_io_bitops.h',
>  	'include/rte_bitmap.h',
>  	'include/rte_class.h',
>  	'include/rte_common.h',
> --
> 2.7.4
>