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

[Morten Brørup]

> -----Original Message-----
> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Joyce Kong (Arm
> Technology China)
> Sent: Wednesday, October 23, 2019 5:08 AM
> 
> > > > -----Original Message-----
> > > > From: dev [mailto:dev-bounces at 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 at 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.
> 
> The PMDs which use the common API now are all 32bit operation, so
> change
> the definition to uint_32_t type instead of individually naming
> functions for
> each type size.

Unless you are certain that all current and future I/O devices only need 32 bit, it should provide variants for different types, like the rte_atomic_xxx API.

There might also be a need to support both big and little endian byte ordering? Perhaps the CPU uses a different byte ordering than the I/O device being accessed through this API. I don't know; I'm only providing half baked feedback on this point.