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From: Stephen Hemminger <stephen@networkplumber.org>
To: Ola Liljedahl <ola.liljedahl@arm.com>
Cc: "Mattias Rönnblom" <mattias.ronnblom@ericsson.com>,
	"dev@dpdk.org" <dev@dpdk.org>,
	"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>,
	"konstantin.ananyev@intel.com" <konstantin.ananyev@intel.com>,
	"mb@smartsharesystems.com" <mb@smartsharesystems.com>
Subject: Re: [PATCH v2] eal: add seqlock
Date: Fri, 1 Apr 2022 14:52:17 -1000	[thread overview]
Message-ID: <20220401145217.66506c78@shemminger-XPS-13-9360> (raw)
In-Reply-To: <1094901f-ee27-8c49-d71f-825ec5bfe2ad@arm.com>

On Thu, 31 Mar 2022 16:53:00 +0200
Ola Liljedahl <ola.liljedahl@arm.com> wrote:

> From: Ola Liljedahl <ola.liljedahl@arm.com>
> To: Mattias Rönnblom <mattias.ronnblom@ericsson.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>,
> "konstantin.ananyev@intel.com" <konstantin.ananyev@intel.com>,
> "mb@smartsharesystems.com" <mb@smartsharesystems.com>,
> "stephen@networkplumber.org" <stephen@networkplumber.org> Subject:
> Re: [PATCH v2] eal: add seqlock Date: Thu, 31 Mar 2022 16:53:00 +0200
> User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
> Thunderbird/91.7.0
> 
> (Thunderbird suddenly refuses to edit in plain text mode, hope the
> mail gets sent as text anyway)
> 
> On 3/31/22 15:38, Mattias Rönnblom wrote:
> 
> > On 2022-03-31 11:04, Ola Liljedahl wrote:  
> >> On 3/31/22 09:46, Mattias Rönnblom wrote:  
> >>> On 2022-03-30 16:26, Mattias Rönnblom wrote:
> >>>  
> <snip>
> >>> Should the rte_seqlock_read_retry() be called
> >>> rte_seqlock_read_end(), or some third alternative? I wanted to
> >>> make clear it's not just a "release the lock" function. You could
> >>> use the|||__attribute__((warn_unused_result)) annotation to make
> >>> clear the return value cannot be ignored, although I'm not sure
> >>> DPDK ever use that attribute.  
> >> We have to decide how to use the seqlock API from the application
> >> perspective.
> >> Your current proposal:
> >> do {
> >>       sn = rte_seqlock_read_begin(&seqlock)
> >>       //read protected data
> >> } while (rte_seqlock_read_retry(&seqlock, sn));
> >>
> >> or perhaps
> >> sn = rte_seqlock_read_lock(&seqlock);
> >> do {
> >>       //read protected data
> >> } while (!rte_seqlock_read_tryunlock(&seqlock, &sn));
> >>
> >> Tryunlock should signal to the user that the unlock operation
> >> might not succeed and something needs to be repeated.
> >>  
> > I like that your proposal is consistent with rwlock API, although I
> > tend to think about a seqlock more like an arbitrary-size atomic
> > load/store, where begin() is the beginning of the read transaction.
> >  
> 
> I can see the evolution of an application where is starts to use
> plain spin locks, moves to reader/writer locks for better performance
> and eventually moves to seqlocks. The usage is the same, only the 
> characteristics (including performance) differ.


The semantics of seqlock in DPDK must be the same as what Linux kernel
does or you are asking for trouble.  It is not a reader-writer lock in
traditional sense.

  reply	other threads:[~2022-04-02  0:52 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 [this message]
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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