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From: fengchengwen <fengchengwen@huawei.com>
To: "Honnappa Nagarahalli" <Honnappa.Nagarahalli@arm.com>,
	"Mattias Rönnblom" <mattias.ronnblom@ericsson.com>,
	"dev@dpdk.org" <dev@dpdk.org>
Cc: "thomas@monjalon.net" <thomas@monjalon.net>,
	David Marchand <david.marchand@redhat.com>,
	"onar.olsen@ericsson.com" <onar.olsen@ericsson.com>,
	nd <nd@arm.com>,
	"konstantin.ananyev@intel.com" <konstantin.ananyev@intel.com>,
	"mb@smartsharesystems.com" <mb@smartsharesystems.com>,
	"stephen@networkplumber.org" <stephen@networkplumber.org>,
	"hofors@lysator.liu.se" <hofors@lysator.liu.se>,
	Ola Liljedahl <Ola.Liljedahl@arm.com>
Subject: Re: [PATCH v5] eal: add seqlock
Date: Fri, 6 May 2022 15:03:12 +0800	[thread overview]
Message-ID: <579809ca-3e26-8b84-be01-fa089ccd6011@huawei.com> (raw)
In-Reply-To: <DBAPR08MB581402392B36E376A1F45FF798C59@DBAPR08MB5814.eurprd08.prod.outlook.com>

On 2022/5/6 13:19, Honnappa Nagarahalli wrote:
> <snip>
> 
>>>>> +__rte_experimental
>>>>> +static inline bool
>>>>> +rte_seqlock_read_retry(const rte_seqlock_t *seqlock, uint32_t
>>>>> +begin_sn) {
>>>>> +	uint32_t end_sn;
>>>>> +
>>>>> +	/* An odd sequence number means the protected data was being
>>>>> +	 * modified already at the point of the rte_seqlock_read_begin()
>>>>> +	 * call.
>>>>> +	 */
>>>>> +	if (unlikely(begin_sn & 1))
>>>>> +		return true;
>>>>> +
>>>>> +	/* make sure the data loads happens before the sn load */
>>>>> +	rte_atomic_thread_fence(__ATOMIC_ACQUIRE);
>>>>
>>>> In ARMv8, the rte_atomic_thread_fence(__ATOMIC_ACQUIRE) and
>>>> rte_smp_rmb() both output 'dma ishld'
>>>> Suggest use rte_smp_rmb(), please see below comment.
>>> rte_smp_xxx APIs are deprecated. Please check [1]
>>>
>>> [1] https://www.dpdk.org/blog/2021/03/26/dpdk-adopts-the-c11-memory-
>> model/
>>
>> Got it, thanks
>>
>> And I have a question about ARM: why can't find the
>> parameter(rte_atomic_thread_fence(?)) corresponding to 'dmb ishst'?
>> I tried __ATOMIC_RELEASE/ACQ_REL/SEQ_CST and can't find it.
> 'dmb ishst' prevents store-store reordering. However, '__atomic_thread_fence' (with various memory ordering) requires more stronger barrier [1].

For this seqlock scenario, I think it's OK to use 'dmb ishst' in rte_seqlock_write_lock()
instead of use rte_atomic_thread_fence(__ATOMIC_RELEASE), but the 'dmb ishst' havn't corresponding
rte_atomic_thread_fence() wrapper, so in this case, we could only use stronger barrier.

Since the community has decided to use the C11 memory mode API, it is probably clear about the
preceding scenarios (using stronger barrier). I have no comment.

> 
> [1] https://preshing.com/20130922/acquire-and-release-fences/
>>
>>>
>>> <snip>
>>>
> 


  reply	other threads:[~2022-05-06  7:03 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
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 [this message]
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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