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From: "Ananyev, Konstantin" <konstantin.ananyev@intel.com>
To: Joyce Kong <joyce.kong@arm.com>, "dev@dpdk.org" <dev@dpdk.org>
Cc: "nd@arm.com" <nd@arm.com>,
	"stephen@networkplumber.org" <stephen@networkplumber.org>,
	"jerin.jacob@caviumnetworks.com" <jerin.jacob@caviumnetworks.com>,
	"thomas@monjalon.net" <thomas@monjalon.net>,
	"honnappa.nagarahalli@arm.com" <honnappa.nagarahalli@arm.com>,
	"gavin.hu@arm.com" <gavin.hu@arm.com>
Subject: Re: [dpdk-dev] [PATCH v6 1/2] eal/ticketlock: ticket based to improve	fairness
Date: Fri, 15 Mar 2019 12:55:59 +0000	[thread overview]
Message-ID: <2601191342CEEE43887BDE71AB977258013655BF89@irsmsx105.ger.corp.intel.com> (raw)
In-Reply-To: <1552632988-80787-2-git-send-email-joyce.kong@arm.com>

Hi,

> diff --git a/lib/librte_eal/common/include/generic/rte_ticketlock.h b/lib/librte_eal/common/include/generic/rte_ticketlock.h
> new file mode 100644
> index 0000000..d63aaaa
> --- /dev/null
> +++ b/lib/librte_eal/common/include/generic/rte_ticketlock.h
> @@ -0,0 +1,308 @@
> +/* SPDX-License-Identifier: BSD-3-Clause
> + * Copyright(c) 2019 Arm Limited
> + */
> +
> +#ifndef _RTE_TICKETLOCK_H_
> +#define _RTE_TICKETLOCK_H_
> +
> +/**
> + * @file
> + *
> + * RTE ticket locks
> + *
> + * This file defines an API for ticket locks, which give each waiting
> + * thread a ticket and take the lock one by one, first come, first
> + * serviced.
> + *
> + * All locks must be initialised before use, and only initialised once.
> + *
> + */
> +
> +#ifdef __cplusplus
> +extern "C" {
> +#endif
> +
> +#include <rte_common.h>
> +#include <rte_lcore.h>
> +#include <rte_pause.h>
> +
> +/**
> + * The rte_ticketlock_t type.
> + */
> +typedef struct {
> +	uint16_t current;
> +	uint16_t next;
> +} rte_ticketlock_t;
> +
> +/**
> + * A static ticketlock initializer.
> + */
> +#define RTE_TICKETLOCK_INITIALIZER { 0 }
> +
> +/**
> + * Initialize the ticketlock to an unlocked state.
> + *
> + * @param tl
> + *   A pointer to the ticketlock.
> + */
> +static inline __rte_experimental void
> +rte_ticketlock_init(rte_ticketlock_t *tl)
> +{
> +	__atomic_store_n(&tl->current, 0, __ATOMIC_RELAXED);
> +	__atomic_store_n(&tl->next, 0, __ATOMIC_RELAXED);
> +}
> +
> +/**
> + * Take the ticketlock.
> + *
> + * @param tl
> + *   A pointer to the ticketlock.
> + */
> +static inline __rte_experimental void
> +rte_ticketlock_lock(rte_ticketlock_t *tl)
> +{
> +	uint16_t me = __atomic_fetch_add(&tl->next, 1, __ATOMIC_RELAXED);
> +	while (__atomic_load_n(&tl->current, __ATOMIC_ACQUIRE) != me)
> +		rte_pause();
> +}
> +
> +/**
> + * Release the ticketlock.
> + *
> + * @param tl
> + *   A pointer to the ticketlock.
> + */
> +static inline __rte_experimental void
> +rte_ticketlock_unlock(rte_ticketlock_t *tl)
> +{
> +	uint16_t i = __atomic_load_n(&tl->current, __ATOMIC_RELAXED);
> +	__atomic_store_n(&tl->current, i+1, __ATOMIC_RELEASE);
> +}
> +
> +/**
> + * Try to take the lock.
> + *
> + * @param tl
> + *   A pointer to the ticketlock.
> + * @return
> + *   1 if the lock is successfully taken; 0 otherwise.
> + */
> +static inline __rte_experimental int
> +rte_ticketlock_trylock(rte_ticketlock_t *tl)
> +{
> +	uint16_t next = __atomic_load_n(&tl->next, __ATOMIC_RELAXED);
> +	uint16_t cur = __atomic_load_n(&tl->current, __ATOMIC_RELAXED);
> +	if (next == cur) {

Probably a naïve one:
Suppose next==cur==1 here, then this thread will experience really long context switch,
so next time it continues its execution tl->next value will wrap-up and will be 1 again, and tl->current==0 (lock held).
I suppose this function will set tl->next=2 and will return a success?
Wouldn't be better here and in _is_locked_ to do load/store for next/current values in one go
(using 32bit op)? 
Konstantin

> +		if (__atomic_compare_exchange_n(&tl->next, &next, next+1,
> +		    0, __ATOMIC_ACQUIRE, __ATOMIC_RELAXED))
> +			return 1;
> +	}
> +
> +	return 0;
> +}
> +
> +/**
> + * Test if the lock is taken.
> + *
> + * @param tl
> + *   A pointer to the ticketlock.
> + * @return
> + *   1 if the lock icurrently taken; 0 otherwise.
> + */
> +static inline __rte_experimental int
> +rte_ticketlock_is_locked(rte_ticketlock_t *tl)
> +{
> +	return (__atomic_load_n(&tl->current, __ATOMIC_ACQUIRE) !=
> +		__atomic_load_n(&tl->next, __ATOMIC_ACQUIRE));
> +}
> +

  parent reply	other threads:[~2019-03-15 12:56 UTC|newest]

Thread overview: 74+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-13 14:46 [dpdk-dev] [PATCH v1] ticketlock: " Gavin Hu
2019-01-14  7:59 ` [dpdk-dev] [EXT] " Jerin Jacob Kollanukkaran
2019-01-14 16:57   ` Gavin Hu (Arm Technology China)
2019-01-14 23:36 ` [dpdk-dev] " Honnappa Nagarahalli
2019-01-18  9:15 ` [dpdk-dev] [PATCH v2 1/2] " Joyce Kong
2019-01-25  8:37   ` [dpdk-dev] [PATCH v3 0/2] ticketlock: implement ticketlock and add test case Joyce Kong
2019-02-19 10:48     ` [dpdk-dev] [PATCH v4 " Joyce Kong
2019-03-11  5:52       ` [dpdk-dev] [PATCH v5 " Joyce Kong
2019-02-19 10:48     ` [dpdk-dev] [PATCH v4 1/2] ticketlock: ticket based to improve fairness Joyce Kong
2019-03-11  5:52       ` [dpdk-dev] [PATCH v5 1/2] eal/ticketlock: " Joyce Kong
2019-03-13  9:41         ` Jerin Jacob Kollanukkaran
2019-03-15  6:57           ` Joyce Kong (Arm Technology China)
2019-03-15  6:57             ` Joyce Kong (Arm Technology China)
2019-03-13 15:36         ` Jerin Jacob Kollanukkaran
2019-03-15  6:58           ` Joyce Kong (Arm Technology China)
2019-03-15  6:58             ` Joyce Kong (Arm Technology China)
2019-02-19 10:48     ` [dpdk-dev] [PATCH v4 2/2] test/ticketlock: add ticket lock test case Joyce Kong
2019-03-11  5:52       ` [dpdk-dev] [PATCH v5 " Joyce Kong
2019-03-13 13:31         ` Jerin Jacob Kollanukkaran
2019-03-15  6:57           ` Joyce Kong (Arm Technology China)
2019-03-15  6:57             ` Joyce Kong (Arm Technology China)
2019-01-25  8:37   ` [dpdk-dev] [PATCH v3 1/2] ticketlock: ticket based to improve fairness Joyce Kong
2019-01-25  8:37   ` [dpdk-dev] [PATCH v3 2/2] test/ticketlock: add ticket lock test case Joyce Kong
2019-03-15  6:56   ` [dpdk-dev] [PATCH v6 0/2] ticketlock: implement ticketlock and add " Joyce Kong
2019-03-15  6:56     ` Joyce Kong
2019-03-15  6:56   ` [dpdk-dev] [PATCH v6 1/2] eal/ticketlock: ticket based to improve fairness Joyce Kong
2019-03-15  6:56     ` Joyce Kong
2019-03-15 12:55     ` Ananyev, Konstantin [this message]
2019-03-15 12:55       ` Ananyev, Konstantin
2019-03-19  9:44       ` Gavin Hu (Arm Technology China)
2019-03-19  9:44         ` Gavin Hu (Arm Technology China)
2019-03-19 10:15         ` Ananyev, Konstantin
2019-03-19 10:15           ` Ananyev, Konstantin
2019-03-20  5:11           ` Gavin Hu (Arm Technology China)
2019-03-20  5:11             ` Gavin Hu (Arm Technology China)
2019-03-20  9:47             ` Ananyev, Konstantin
2019-03-20  9:47               ` Ananyev, Konstantin
2019-03-22  2:04               ` Gavin Hu (Arm Technology China)
2019-03-22  2:04                 ` Gavin Hu (Arm Technology China)
2019-03-15  6:56   ` [dpdk-dev] [PATCH v6 2/2] test/ticketlock: add ticket lock test case Joyce Kong
2019-03-15  6:56     ` Joyce Kong
2019-03-21  9:13   ` [dpdk-dev] [PATCH v7 0/3] ticketlock: implement ticketlock and add " Joyce Kong
2019-03-21  9:13     ` Joyce Kong
2019-03-21  9:13   ` [dpdk-dev] [PATCH v7 2/3] eal/ticketlock: enable generic ticketlock on all arch Joyce Kong
2019-03-21  9:13     ` Joyce Kong
2019-03-21  9:13   ` [dpdk-dev] [PATCH v7 3/3] test/ticketlock: add ticket lock test case Joyce Kong
2019-03-21  9:13     ` Joyce Kong
2019-03-22 11:38     ` Ananyev, Konstantin
2019-03-22 11:38       ` Ananyev, Konstantin
2019-03-25 10:25       ` Joyce Kong (Arm Technology China)
2019-03-25 10:25         ` Joyce Kong (Arm Technology China)
2019-03-21  9:15   ` [dpdk-dev] [PATCH v7 1/3] eal/ticketlock: ticket based to improve fairness Joyce Kong
2019-03-21  9:15     ` Joyce Kong
2019-03-22 10:56     ` Ananyev, Konstantin
2019-03-22 10:56       ` Ananyev, Konstantin
2019-03-25 11:11   ` [dpdk-dev] [PATCH v8 0/3] ticketlock: implement ticketlock and add test case Joyce Kong
2019-03-25 11:11     ` Joyce Kong
2019-03-27 11:20     ` Ananyev, Konstantin
2019-03-27 11:20       ` Ananyev, Konstantin
2019-03-28 14:02       ` Thomas Monjalon
2019-03-28 14:02         ` Thomas Monjalon
2019-03-25 11:11   ` [dpdk-dev] [PATCH v8 1/3] eal/ticketlock: ticket based to improve fairness Joyce Kong
2019-03-25 11:11     ` Joyce Kong
2019-03-25 11:11   ` [dpdk-dev] [PATCH v8 2/3] eal/ticketlock: enable generic ticketlock on all arch Joyce Kong
2019-03-25 11:11     ` Joyce Kong
2019-03-25 11:11   ` [dpdk-dev] [PATCH v8 3/3] test/ticketlock: add ticket lock test case Joyce Kong
2019-03-25 11:11     ` Joyce Kong
2019-04-08 20:18     ` David Marchand
2019-04-08 20:18       ` David Marchand
2019-04-14 20:37       ` Thomas Monjalon
2019-04-14 20:37         ` Thomas Monjalon
2019-04-15  9:07         ` Joyce Kong (Arm Technology China)
2019-04-15  9:07           ` Joyce Kong (Arm Technology China)
2019-01-18  9:15 ` [dpdk-dev] [PATCH v2 2/2] " Joyce Kong

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