From: Ola Liljedahl <ola.liljedahl@arm.com>
To: "Mattias Rönnblom" <mattias.ronnblom@ericsson.com>, dev@dpdk.org
Cc: Thomas Monjalon <thomas@monjalon.net>,
David Marchand <david.marchand@redhat.com>,
onar.olsen@ericsson.com, Honnappa.Nagarahalli@arm.com,
nd@arm.com, konstantin.ananyev@intel.com,
mb@smartsharesystems.com, stephen@networkplumber.org
Subject: Re: [PATCH v3] eal: add seqlock
Date: Sat, 2 Apr 2022 20:15:59 +0200 [thread overview]
Message-ID: <3efba44b-1a2e-831e-1e2c-782639d83c24@arm.com> (raw)
In-Reply-To: <20220401150749.136921-1-mattias.ronnblom@ericsson.com>
On 4/1/22 17:07, Mattias Rönnblom wrote:
> +
> +/**
> + * End a read-side critical section.
> + *
> + * A call to this function marks the end of a read-side critical
> + * section, for @p seqlock. The application must supply the sequence
> + * number produced by the corresponding rte_seqlock_read_lock() (or,
> + * in case of a retry, the rte_seqlock_tryunlock()) call.
> + *
> + * After this function has been called, the caller should not access
> + * the protected data.
> + *
> + * In case this function returns true, the just-read data was
> + * consistent and the set of atomic and non-atomic load operations
> + * performed between rte_seqlock_read_lock() and
> + * rte_seqlock_read_tryunlock() were atomic, as a whole.
> + *
> + * In case rte_seqlock_read_tryunlock() returns false, the data was
> + * modified as it was being read and may be inconsistent, and thus
> + * should be discarded. The @p begin_sn is updated with the
> + * now-current sequence number.
> + *
> + * @param seqlock
> + * A pointer to the seqlock.
> + * @param begin_sn
> + * The seqlock sequence number returned by
> + * rte_seqlock_read_lock() (potentially updated in subsequent
> + * rte_seqlock_read_tryunlock() calls) for this critical section.
> + * @return
> + * true or false, if the just-read seqlock-protected data was consistent
> + * or inconsistent, respectively, at the time it was read.
> + *
> + * @see rte_seqlock_read_lock()
> + */
> +__rte_experimental
> +static inline bool
> +rte_seqlock_read_tryunlock(const rte_seqlock_t *seqlock, uint32_t *begin_sn)
> +{
> + uint32_t end_sn;
> +
> + /* make sure the data loads happens before the sn load */
> + rte_atomic_thread_fence(__ATOMIC_ACQUIRE);
> +
> + end_sn = __atomic_load_n(&seqlock->sn, __ATOMIC_RELAXED);
Since we are reading and potentially returning the sequence number here
(repeating the read of the protected data), we need to use load-acquire.
I assume it is not expected that the user will call
rte_seqlock_read_lock() again.
Seeing this implementation, I might actually prefer the original
implementation, I think it is cleaner. But I would like for the begin
function also to wait for an even sequence number, the end function
would only have to check for same sequence number, this might improve
performance a little bit as readers won't perform one or several broken
reads while a write is in progress. The function names are a different
thing though.
The writer side behaves much more like a lock with mutual exclusion so
write_lock/write_unlock makes sense.
> +
> + if (unlikely(end_sn & 1 || *begin_sn != end_sn)) {
> + *begin_sn = end_sn;
> + return false;
> + }
> +
> + return true;
> +}
> +
next prev parent reply other threads:[~2022-04-02 18:16 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 [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=3efba44b-1a2e-831e-1e2c-782639d83c24@arm.com \
--to=ola.liljedahl@arm.com \
--cc=Honnappa.Nagarahalli@arm.com \
--cc=david.marchand@redhat.com \
--cc=dev@dpdk.org \
--cc=konstantin.ananyev@intel.com \
--cc=mattias.ronnblom@ericsson.com \
--cc=mb@smartsharesystems.com \
--cc=nd@arm.com \
--cc=onar.olsen@ericsson.com \
--cc=stephen@networkplumber.org \
--cc=thomas@monjalon.net \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).