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From: Ruifeng Wang <Ruifeng.Wang@arm.com>
To: Stephen Hemminger <stephen@networkplumber.org>, "dev@dpdk.org"
<dev@dpdk.org>
CC: nd <nd@arm.com>
Thread-Topic: [dpdk-dev] [PATCH v1] eal: add ticket based reader writer lock
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Subject: Re: [dpdk-dev] [PATCH v1] eal: add ticket based reader writer lock
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Errors-To: dev-bounces@dpdk.org
Sender: "dev" <dev-bounces@dpdk.org>
> -----Original Message-----
> From: dev <dev-bounces@dpdk.org> On Behalf Of Stephen Hemminger
> Sent: Friday, January 15, 2021 1:35 AM
> To: dev@dpdk.org
> Cc: Stephen Hemminger <stephen@networkplumber.org>
> Subject: [dpdk-dev] [PATCH v1] eal: add ticket based reader writer lock
>=20
> This patch implements a reader/writer ticket lock.
> This lock type acts like rte_rwlock() but uses a ticket algorithm and are=
fair for
> multiple writers and readers.
> Writers have priority over readers.
The lock is ticket based to be fair. So writers should have no priority?
>=20
> The tests are just a clone of existing rte_rwlock with test and function =
names
> changed. So the new ticket rwlocks should be drop in replacement for most
> users.
>=20
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> ---
> Ps: I have additional tests for rwlock that test for fairness.
> Would these be valuable?
>=20
> app/test/autotest_data.py | 6 +
> app/test/meson.build | 5 +
> app/test/test_ticket_rwlock.c | 554 ++++++++++++++++++
> doc/api/doxy-api-index.md | 1 +
> lib/librte_eal/arm/include/meson.build | 1 +
> .../arm/include/rte_ticket_rwlock.h | 22 +
> .../include/generic/rte_ticket_rwlock.h | 218 +++++++
> lib/librte_eal/include/meson.build | 1 +
> lib/librte_eal/ppc/include/meson.build | 1 +
> .../ppc/include/rte_ticket_rwlock.h | 18 +
> lib/librte_eal/x86/include/meson.build | 1 +
> .../x86/include/rte_ticket_rwlock.h | 18 +
> 12 files changed, 846 insertions(+)
> create mode 100644 app/test/test_ticket_rwlock.c create mode 100644
> lib/librte_eal/arm/include/rte_ticket_rwlock.h
> create mode 100644 lib/librte_eal/include/generic/rte_ticket_rwlock.h
> create mode 100644 lib/librte_eal/ppc/include/rte_ticket_rwlock.h
> create mode 100644 lib/librte_eal/x86/include/rte_ticket_rwlock.h
>=20
<snip>
> diff --git a/lib/librte_eal/include/generic/rte_ticket_rwlock.h
> b/lib/librte_eal/include/generic/rte_ticket_rwlock.h
> new file mode 100644
> index 000000000000..b3637358c1f7
> --- /dev/null
> +++ b/lib/librte_eal/include/generic/rte_ticket_rwlock.h
> @@ -0,0 +1,218 @@
> +/* SPDX-License-Identifier: BSD-3-Clause
> + * Copyright(c) 2021 Microsoft Corporation */
> +
> +#ifndef _RTE_TICKET_RWLOCK_H_
> +#define _RTE_TICKET_RWLOCK_H_
> +
> +/**
> + * @file
> + *
> + * Ticket based reader/writer lock
> + *
> + * This file defines an API for ticket style read-write locks.
> + * This types of lock act like rte_rwlock but provide fairness
> + * and requests are handled first come, first serviced.
> + *
> + * All locks must be initialized before use, and only initialized once.
> + *
> + * References:
> + * "Spinlocks and Read-Write Locks"
> + * http://locklessinc.com/articles/locks/
> + * "Scalable Read-Writer Synchronization for Shared-Memory
> Multiprocessors"
> + *
> https://www.cs.rochester.edu/research/synchronization/pseudocode/rw.ht
> ml
> + */
> +
> +#ifdef __cplusplus
> +extern "C" {
> +#endif
> +
> +typedef union {
> + uint64_t tickets;
> + struct {
> + union {
> + struct {
> + uint16_t write; /* current writer */
> + uint16_t read; /* current reader */
> + };
> + uint32_t readwrite; /* atomic for both read and
> write */
> + };
> + uint16_t next; /* next ticket */
> + };
> +} rte_rwticketlock_t;
> +
> +/**
> + * A static rwticket initializer.
> + */
> +#define RTE_RWTICKETLOCK_INITIALIZER { 0 }
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + *
> + * Initialize the rwticketlock to an unlocked state.
> + *
> + * @param rwl
> + * A pointer to the rwticketlock structure.
> + */
> +__rte_experimental
> +static inline void
> +rte_rwticketlock_init(rte_rwticketlock_t *rwl) {
> + rwl->tickets =3D 0;
> +}
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + * Take a write lock. Loop until the lock is held.
> + *
> + * @param rwl
> + * A pointer to a rwticketlock structure.
> + */
> +__rte_experimental
> +static inline void
> +rte_rwticket_write_lock(rte_rwticketlock_t *rwl) {
> + uint16_t me;
> +
> + me =3D __atomic_fetch_add(&rwl->next, 1, __ATOMIC_RELAXED);
> + rte_wait_until_equal_16(&rwl->write, me, __ATOMIC_ACQUIRE); }
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + *
> + * Try to take a write lock.
> + *
> + * @param rwl
> + * A pointer to a rwticketlock structure.
> + * @return
> + * - zero if the lock is successfully taken
> + * - -EBUSY if lock could not be acquired for writing because
> + * it was already locked for reading or writing
> + */
> +__rte_experimental
> +static inline int
> +rte_rwticket_write_trylock(rte_rwticketlock_t *rwl) {
> + rte_rwticketlock_t old, new;
> +
> + old.tickets =3D __atomic_load_n(&rwl->tickets, __ATOMIC_RELAXED);
> + if (old.write !=3D old.next)
> + return -EBUSY;
> +
> + new.tickets =3D old.tickets;
> + new.next =3D old.next + 1;
> + if (__atomic_compare_exchange_n(&rwl->tickets, &old.tickets,
> new.tickets,
> + 0, __ATOMIC_ACQUIRE,
> __ATOMIC_RELAXED))
> + return 0;
> + else
> + return -EBUSY;
> +}
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + *
> + * Release a write lock.
> + *
> + * @param rwl
> + * A pointer to a rwticketlock structure.
> + */
> +__rte_experimental
> +static inline void
> +rte_rwticket_write_unlock(rte_rwticketlock_t *rwl) {
> + rte_rwticketlock_t t;
> +
> + t.tickets =3D __atomic_load_n(&rwl->tickets, __ATOMIC_RELAXED);
> + t.write++;
> + t.read++;
> + __atomic_store_n(&rwl->readwrite, t.readwrite,
> __ATOMIC_RELEASE); }
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + *
> + *
> + * Take a read lock. Loop until the lock is held.
> + *
> + * @param l
Nit, 'rwl'.
> + * A pointer to a rwticketlock structure.
> + */
> +__rte_experimental
> +static inline void
> +rte_rwticket_read_lock(rte_rwticketlock_t *rwl) {
> + uint16_t me;
> +
> + me =3D __atomic_fetch_add(&rwl->next, 1, __ATOMIC_RELAXED);
> + rte_wait_until_equal_16(&rwl->read, me, __ATOMIC_ACQUIRE);
> + __atomic_fetch_add(&rwl->read, 1, __ATOMIC_RELAXED); }
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + *
> + * Try to take a read lock.
> + *
> + * @param rwl
> + * A pointer to a rwticketlock structure.
> + *
> + * @return
> + * - zero if the lock is successfully taken
> + * - -EBUSY if lock could not be acquired for reading because a
> + * writer holds the lock
> + */
> +__rte_experimental
> +static inline int
> +rte_rwticket_read_trylock(rte_rwticketlock_t *rwl) {
> + rte_rwticketlock_t old, new;
> + int success;
> +
> + old.tickets =3D __atomic_load_n(&rwl->tickets, __ATOMIC_RELAXED);
> +
> + do {
> + uint16_t me =3D old.next; /* this is our ticket */
When __atomic_compare_exchange_n fails, old.tickets needs a reload.
=20
> +
> + /* does writer have the lock now? */
> + if (old.read !=3D me && old.write !=3D me)
Check (old.read !=3D me) should be enough?
> + return -EBUSY;
> +
> + /* expect to be the next reader */
> + new.tickets =3D old.tickets;
> + old.read =3D me;
This line is unnecessary?
> + new.read =3D new.next =3D me + 1;
> + success =3D __atomic_compare_exchange_n(&rwl->tickets,
> &old.tickets, new.tickets,
> + 0, __ATOMIC_ACQUIRE,
> __ATOMIC_RELAXED);
> + } while (!success);
> +
> + return 0;
> +}
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + *
> + * Release a read lock.
> + *
> + * @param rwl
> + * A pointer to the rwticketlock structure.
> + */
> +__rte_experimental
> +static inline void
> +rte_rwticket_read_unlock(rte_rwticketlock_t *rwl) {
> + __atomic_add_fetch(&rwl->write, 1, __ATOMIC_RELEASE); }
> +
> +#ifdef __cplusplus
> +}
> +#endif
> +
> +#endif /* _RTE_TICKET_RWLOCK_H_ */
> diff --git a/lib/librte_eal/include/meson.build
> b/lib/librte_eal/include/meson.build
> index 0dea342e1deb..fe5c19748926 100644
> --- a/lib/librte_eal/include/meson.build
> +++ b/lib/librte_eal/include/meson.build
> @@ -65,6 +65,7 @@ generic_headers =3D files(
> 'generic/rte_rwlock.h',
> 'generic/rte_spinlock.h',
> 'generic/rte_ticketlock.h',
> + 'generic/rte_ticket_rwlock.h',
> 'generic/rte_vect.h',
> )
> install_headers(generic_headers, subdir: 'generic') diff --git
> a/lib/librte_eal/ppc/include/meson.build
> b/lib/librte_eal/ppc/include/meson.build
> index dae40ede546e..0bc560327749 100644
> --- a/lib/librte_eal/ppc/include/meson.build
> +++ b/lib/librte_eal/ppc/include/meson.build
> @@ -16,6 +16,7 @@ arch_headers =3D files(
> 'rte_rwlock.h',
> 'rte_spinlock.h',
> 'rte_ticketlock.h',
> + 'rte_ticket_rwlock.h',
> 'rte_vect.h',
> )
> install_headers(arch_headers, subdir: get_option('include_subdir_arch'))
> diff --git a/lib/librte_eal/ppc/include/rte_ticket_rwlock.h
> b/lib/librte_eal/ppc/include/rte_ticket_rwlock.h
> new file mode 100644
> index 000000000000..4768d5bfa8ef
> --- /dev/null
> +++ b/lib/librte_eal/ppc/include/rte_ticket_rwlock.h
> @@ -0,0 +1,18 @@
> +/* SPDX-License-Identifier: BSD-3-Clause
> + * Copyright(c) 2021 Microsoft Corporation */
> +
> +#ifndef _RTE_FAIR_RWLOCK_PPC_64_H_
> +#define _RTE_FAIR_RWLOCK_PPC_64_H_
> +
> +#ifdef __cplusplus
> +extern "C" {
> +#endif
> +
> +#include "generic/rte_ticket_rwlock.h"
> +
> +#ifdef __cplusplus
> +}
> +#endif
> +
> +#endif /* _RTE_FAIR_RWLOCK_PPC_64_H_ */
> diff --git a/lib/librte_eal/x86/include/meson.build
> b/lib/librte_eal/x86/include/meson.build
> index 549cc21a42ed..e9169f0d1da5 100644
> --- a/lib/librte_eal/x86/include/meson.build
> +++ b/lib/librte_eal/x86/include/meson.build
> @@ -20,6 +20,7 @@ arch_headers =3D files(
> 'rte_rwlock.h',
> 'rte_spinlock.h',
> 'rte_ticketlock.h',
> + 'rte_ticket_rwlock.h',
> 'rte_vect.h',
> )
> install_headers(arch_headers, subdir: get_option('include_subdir_arch'))
> diff --git a/lib/librte_eal/x86/include/rte_ticket_rwlock.h
> b/lib/librte_eal/x86/include/rte_ticket_rwlock.h
> new file mode 100644
> index 000000000000..83c8bd0899d3
> --- /dev/null
> +++ b/lib/librte_eal/x86/include/rte_ticket_rwlock.h
> @@ -0,0 +1,18 @@
> +/* SPDX-License-Identifier: BSD-3-Clause
> + * Copyright(c) 2021 Microsoft Corporation */
> +
> +#ifndef _RTE_FAIR_RWLOCK_X86_64_H_
> +#define _RTE_FAIR_RWLOCK_X86_64_H_
> +
> +#ifdef __cplusplus
> +extern "C" {
> +#endif
> +
> +#include "generic/rte_ticket_rwlock.h"
> +
> +#ifdef __cplusplus
> +}
> +#endif
> +
> +#endif /* _RTE_FAIR_RWLOCK_X86_64_H_ */
> --
> 2.29.2