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From: "Mattias Rönnblom" <mattias.ronnblom@ericsson.com>
To: "Ananyev, Konstantin" <konstantin.ananyev@intel.com>,
	"dev@dpdk.org" <dev@dpdk.org>
Cc: Thomas Monjalon <thomas@monjalon.net>,
	David Marchand <david.marchand@redhat.com>,
	Onar Olsen <onar.olsen@ericsson.com>,
	"Honnappa.Nagarahalli@arm.com" <Honnappa.Nagarahalli@arm.com>,
	"nd@arm.com" <nd@arm.com>,
	"mb@smartsharesystems.com" <mb@smartsharesystems.com>,
	"stephen@networkplumber.org" <stephen@networkplumber.org>,
	Ola Liljedahl <ola.liljedahl@arm.com>
Subject: Re: [RFC] eal: add seqlock
Date: Sun, 27 Mar 2022 17:42:28 +0000	[thread overview]
Message-ID: <77168168-eadb-9a0b-b51e-9ccdf8ad7230@ericsson.com> (raw)
In-Reply-To: <DM6PR11MB44916E6635D263B2B3A6D8B29A1C9@DM6PR11MB4491.namprd11.prod.outlook.com>

On 2022-03-27 16:49, Ananyev, Konstantin wrote:
>> diff --git a/lib/eal/include/meson.build b/lib/eal/include/meson.build
>> index 9700494816..48df5f1a21 100644
>> --- a/lib/eal/include/meson.build
>> +++ b/lib/eal/include/meson.build
>> @@ -36,6 +36,7 @@ headers += files(
>>           'rte_per_lcore.h',
>>           'rte_random.h',
>>           'rte_reciprocal.h',
>> +        'rte_seqlock.h',
>>           'rte_service.h',
>>           'rte_service_component.h',
>>           'rte_string_fns.h',
>> diff --git a/lib/eal/include/rte_seqlock.h b/lib/eal/include/rte_seqlock.h
>> new file mode 100644
>> index 0000000000..b975ca848a
>> --- /dev/null
>> +++ b/lib/eal/include/rte_seqlock.h
>> @@ -0,0 +1,84 @@
>> +/* SPDX-License-Identifier: BSD-3-Clause
>> + * Copyright(c) 2022 Ericsson AB
>> + */
>> +
>> +#ifndef _RTE_SEQLOCK_H_
>> +#define _RTE_SEQLOCK_H_
>> +
>> +#include <stdbool.h>
>> +#include <stdint.h>
>> +
>> +#include <rte_atomic.h>
>> +#include <rte_branch_prediction.h>
>> +#include <rte_spinlock.h>
>> +
>> +struct rte_seqlock {
>> +	uint64_t sn;
>> +	rte_spinlock_t lock;
>> +};
>> +
>> +typedef struct rte_seqlock rte_seqlock_t;
>> +
>> +__rte_experimental
>> +void
>> +rte_seqlock_init(rte_seqlock_t *seqlock);
> Probably worth to have static initializer too.
>

I will add that in the next version, thanks.

>> +
>> +__rte_experimental
>> +static inline uint64_t
>> +rte_seqlock_read_begin(const rte_seqlock_t *seqlock)
>> +{
>> +	/* __ATOMIC_ACQUIRE to prevent loads after (in program order)
>> +	 * from happening before the sn load. Syncronizes-with the
>> +	 * store release in rte_seqlock_end().
>> +	 */
>> +	return __atomic_load_n(&seqlock->sn, __ATOMIC_ACQUIRE);
>> +}
>> +
>> +__rte_experimental
>> +static inline bool
>> +rte_seqlock_read_retry(const rte_seqlock_t *seqlock, uint64_t begin_sn)
>> +{
>> +	uint64_t end_sn;
>> +
>> +	/* make sure the data loads happens before the sn load */
>> +	rte_atomic_thread_fence(__ATOMIC_ACQUIRE);
> That's sort of 'read_end' correct?
> If so, shouldn't it be '__ATOMIC_RELEASE' instead here,
> and
> end_sn = __atomic_load_n(..., (__ATOMIC_ACQUIRE)
> on the line below?

A release fence prevents reordering of stores. The reader doesn't do any 
stores, so I don't understand why you would use a release fence here. 
Could you elaborate?

>> +
>> +	end_sn = __atomic_load_n(&seqlock->sn, __ATOMIC_RELAXED);
>> +
>> +	return unlikely(begin_sn & 1 || begin_sn != end_sn);
>> +}
>> +
>> +__rte_experimental
>> +static inline void
>> +rte_seqlock_write_begin(rte_seqlock_t *seqlock)
>> +{
>> +	uint64_t sn;
>> +
>> +	/* to synchronize with other writers */
>> +	rte_spinlock_lock(&seqlock->lock);
>> +
>> +	sn = seqlock->sn + 1;
>> +
>> +	__atomic_store_n(&seqlock->sn, sn, __ATOMIC_RELAXED);
>> +
>> +	/* __ATOMIC_RELEASE to prevent stores after (in program order)
>> +	 * from happening before the sn store.
>> +	 */
>> +	rte_atomic_thread_fence(__ATOMIC_RELEASE);
> I think it needs to be '__ATOMIC_ACQUIRE' here instead of '__ATOMIC_RELEASE'.

Please elaborate on why.

>> +}
>> +
>> +__rte_experimental
>> +static inline void
>> +rte_seqlock_write_end(rte_seqlock_t *seqlock)
>> +{
>> +	uint64_t sn;
>> +
>> +	sn = seqlock->sn + 1;
>> +
>> +	/* synchronizes-with the load acquire in rte_seqlock_begin() */
>> +	__atomic_store_n(&seqlock->sn, sn, __ATOMIC_RELEASE);
>> +
>> +	rte_spinlock_unlock(&seqlock->lock);
>> +}
>> +


  reply	other threads:[~2022-03-27 17:42 UTC|newest]

Thread overview: 104+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-22 16:10 DPDK seqlock Mattias Rönnblom
2022-03-22 16:46 ` Ananyev, Konstantin
2022-03-24  4:52   ` Honnappa Nagarahalli
2022-03-24  5:06     ` Stephen Hemminger
2022-03-24 11:34     ` Mattias Rönnblom
2022-03-25 20:24       ` [RFC] eal: add seqlock Mattias Rönnblom
2022-03-25 21:10         ` Stephen Hemminger
2022-03-26 14:57           ` Mattias Rönnblom
2022-03-27 14:49         ` Ananyev, Konstantin
2022-03-27 17:42           ` Mattias Rönnblom [this message]
2022-03-28 10:53             ` Ananyev, Konstantin
2022-03-28 14:06               ` Ola Liljedahl
2022-03-29  8:32                 ` Mattias Rönnblom
2022-03-29 13:20                   ` Ananyev, Konstantin
2022-03-30 10:07                     ` [PATCH] " Mattias Rönnblom
2022-03-30 10:50                       ` Morten Brørup
2022-03-30 11:24                         ` Tyler Retzlaff
2022-03-30 11:25                         ` Mattias Rönnblom
2022-03-30 14:26                         ` [PATCH v2] " Mattias Rönnblom
2022-03-31  7:46                           ` Mattias Rönnblom
2022-03-31  9:04                             ` Ola Liljedahl
2022-03-31  9:25                               ` Morten Brørup
2022-03-31  9:38                                 ` Ola Liljedahl
2022-03-31 10:03                                   ` Morten Brørup
2022-03-31 11:44                                     ` Ola Liljedahl
2022-03-31 11:50                                       ` Morten Brørup
2022-03-31 14:02                                       ` Mattias Rönnblom
2022-04-01 15:07                                         ` [PATCH v3] " Mattias Rönnblom
2022-04-02  0:21                                           ` Honnappa Nagarahalli
2022-04-02 11:01                                             ` Morten Brørup
2022-04-02 19:38                                               ` Honnappa Nagarahalli
2022-04-10 13:51                                                 ` [RFC 1/3] eal: add macro to warn for unused function return values Mattias Rönnblom
2022-04-10 13:51                                                   ` [RFC 2/3] eal: emit warning for unused trylock return value Mattias Rönnblom
2022-04-10 13:51                                                   ` [RFC 3/3] examples/bond: fix invalid use of trylock Mattias Rönnblom
2022-04-11  1:01                                                     ` Min Hu (Connor)
2022-04-11 14:32                                                       ` Mattias Rönnblom
2022-04-11 11:25                                                     ` David Marchand
2022-04-11 14:33                                                       ` Mattias Rönnblom
2022-04-10 18:02                                                   ` [RFC 1/3] eal: add macro to warn for unused function return values Stephen Hemminger
2022-04-10 18:50                                                     ` Mattias Rönnblom
2022-04-11  7:17                                                   ` Morten Brørup
2022-04-11 14:29                                                     ` Mattias Rönnblom
2022-04-11  9:16                                                   ` Bruce Richardson
2022-04-11 14:27                                                     ` Mattias Rönnblom
2022-04-11 15:15                                                     ` [PATCH " Mattias Rönnblom
2022-04-11 15:15                                                       ` [PATCH 2/3] eal: emit warning for unused trylock return value Mattias Rönnblom
2022-04-11 15:29                                                         ` Morten Brørup
2022-04-11 15:15                                                       ` [PATCH 3/3] examples/bond: fix invalid use of trylock Mattias Rönnblom
2022-04-14 12:06                                                         ` David Marchand
2022-04-11 15:25                                                       ` [PATCH 1/3] eal: add macro to warn for unused function return values Morten Brørup
2022-04-11 18:24                                                     ` [RFC " Tyler Retzlaff
2022-04-03  6:10                                             ` [PATCH v3] eal: add seqlock Mattias Rönnblom
2022-04-03 17:27                                               ` Honnappa Nagarahalli
2022-04-03 18:37                                                 ` Ola Liljedahl
2022-04-04 21:56                                                   ` Honnappa Nagarahalli
2022-04-03  6:33                                             ` Mattias Rönnblom
2022-04-03 17:37                                               ` Honnappa Nagarahalli
2022-04-08 13:45                                                 ` Mattias Rönnblom
2022-04-02 18:15                                           ` Ola Liljedahl
2022-04-02 19:31                                             ` Honnappa Nagarahalli
2022-04-02 20:36                                               ` Morten Brørup
2022-04-02 22:01                                                 ` Honnappa Nagarahalli
2022-04-03 18:11                                               ` Ola Liljedahl
2022-04-03  6:51                                             ` Mattias Rönnblom
2022-03-31 13:51                                 ` [PATCH v2] " Mattias Rönnblom
2022-04-02  0:54                                   ` Stephen Hemminger
2022-04-02 10:25                                     ` Morten Brørup
2022-04-02 17:43                                       ` Ola Liljedahl
2022-03-31 13:38                               ` Mattias Rönnblom
2022-03-31 14:53                                 ` Ola Liljedahl
2022-04-02  0:52                                   ` Stephen Hemminger
2022-04-03  6:23                                     ` Mattias Rönnblom
2022-04-02  0:50                           ` Stephen Hemminger
2022-04-02 17:54                             ` Ola Liljedahl
2022-04-02 19:37                               ` Honnappa Nagarahalli
2022-04-05 20:16                           ` Stephen Hemminger
2022-04-08 13:50                             ` Mattias Rönnblom
2022-04-08 14:24                               ` [PATCH v4] " Mattias Rönnblom
2022-04-08 15:17                                 ` Stephen Hemminger
2022-04-08 16:24                                   ` Mattias Rönnblom
2022-04-08 15:19                                 ` Stephen Hemminger
2022-04-08 16:37                                   ` Mattias Rönnblom
2022-04-08 16:48                                 ` Mattias Rönnblom
2022-04-12 17:27                                 ` Ananyev, Konstantin
2022-04-28 10:28                                 ` David Marchand
2022-05-01 13:46                                   ` Mattias Rönnblom
2022-05-01 14:03                                     ` [PATCH v5] " Mattias Rönnblom
2022-05-01 14:22                                       ` Mattias Rönnblom
2022-05-02  6:47                                         ` David Marchand
2022-05-01 20:17                                       ` Stephen Hemminger
2022-05-02  4:51                                         ` Mattias Rönnblom
2022-05-06  1:26                                       ` fengchengwen
2022-05-06  1:33                                         ` Honnappa Nagarahalli
2022-05-06  4:17                                           ` fengchengwen
2022-05-06  5:19                                             ` Honnappa Nagarahalli
2022-05-06  7:03                                               ` fengchengwen
2022-05-08 11:56                                         ` Mattias Rönnblom
2022-05-08 12:12                                           ` [PATCH v6] " Mattias Rönnblom
2022-05-08 16:10                                             ` Stephen Hemminger
2022-05-08 19:40                                               ` Mattias Rönnblom
2022-05-09  3:48                                                 ` Stephen Hemminger
2022-05-09  6:26                                                   ` Morten Brørup
2022-05-13  6:27                                                   ` Mattias Rönnblom
2022-03-23 12:04 ` DPDK seqlock Morten Brørup

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