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

["Joyce Kong (Arm Technology China)" <Joyce.Kong@arm.com>]

Hi Morten,

> -----Original Message-----
> From: Morten Brørup <mb@smartsharesystems.com>
> Sent: Thursday, October 17, 2019 9:32 PM
> To: Joyce Kong (Arm Technology China) <Joyce.Kong@arm.com>;
> dev@dpdk.org
> Cc: nd <nd@arm.com>; thomas@monjalon.net; jerinj@marvell.com;
> ravi1.kumar@amd.com; xuanziyang2@huawei.com;
> cloud.wangxiaoyun@huawei.com; zhouguoyang@huawei.com;
> rmody@marvell.com; shshaikh@marvell.com; Honnappa Nagarahalli
> <Honnappa.Nagarahalli@arm.com>; Gavin Hu (Arm Technology China)
> <Gavin.Hu@arm.com>; Stephen Hemminger
> <stephen@networkplumber.org>
> Subject: RE: [dpdk-dev] [PATCH v1 1/5] lib/eal: implement the family of rte
> bitoperation APIs
> 
> > -----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); }
> 
You re right, it's better to use __atomic_xx here to keep the consistent with other APIs.

> > +
> > +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().
> 
Good suggestion! And will do this in next version.

> Med venlig hilsen / kind regards
> - Morten Brørup