From: "Mattias Rönnblom" <mattias.ronnblom@ericsson.com>
To: Jerin Jacob <jerinjacobk@gmail.com>
Cc: "jerinj@marvell.com" <jerinj@marvell.com>,
"hofors@lysator.liu.se" <hofors@lysator.liu.se>,
"dev@dpdk.org" <dev@dpdk.org>,
"Morten Brørup" <mb@smartsharesystems.com>
Subject: Re: [PATCH v3] eventdev: avoid non-burst shortcut for variable-size bursts
Date: Fri, 12 May 2023 13:15:25 +0000 [thread overview]
Message-ID: <7c0013e1-d11b-2ad0-04b9-73be426d4719@ericsson.com> (raw)
In-Reply-To: <CALBAE1ONk9pcvdMwHnKsHOKvTXbYhFf=PZU1Ks8phH=ix0T0OQ@mail.gmail.com>
On 2023-05-12 13:59, Jerin Jacob wrote:
> On Thu, May 11, 2023 at 2:00 PM Mattias Rönnblom
> <mattias.ronnblom@ericsson.com> wrote:
>>
>> Use non-burst event enqueue and dequeue calls from burst enqueue and
>> dequeue only when the burst size is compile-time constant (and equal
>> to one).
>>
>> Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
>>
>> ---
>>
>> v3: Actually include the change v2 claimed to contain.
>> v2: Wrap builtin call in __extension__, to avoid compiler warnings if
>> application is compiled with -pedantic. (Morten Brørup)
>> ---
>> lib/eventdev/rte_eventdev.h | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/lib/eventdev/rte_eventdev.h b/lib/eventdev/rte_eventdev.h
>> index a90e23ac8b..a471caeb6d 100644
>> --- a/lib/eventdev/rte_eventdev.h
>> +++ b/lib/eventdev/rte_eventdev.h
>> @@ -1944,7 +1944,7 @@ __rte_event_enqueue_burst(uint8_t dev_id, uint8_t port_id,
>> * Allow zero cost non burst mode routine invocation if application
>> * requests nb_events as const one
>> */
>> - if (nb_events == 1)
>> + if (__extension__(__builtin_constant_p(nb_events)) && nb_events == 1)
>
> "Why" part is not clear from the commit message. Is this to avoid
> nb_events read if it is built-in const.
The __builtin_constant_p() is introduced to avoid having the compiler
generate a conditional branch and two different code paths in case
nb_elem is a run-time variable.
In particular, this matters if nb_elems is run-time variable and varies
between 1 and some larger value.
I should have mention this in the commit message.
A very slight performance improvement. It also makes the code better
match the comment, imo. Zero cost for const one enqueues, but no impact
non-compile-time-constant-length enqueues.
Feel free to ignore.
> If so, check should be following. Right?
>
> if (__extension__((__builtin_constant_p(nb_events)) && nb_events == 1)
> || nb_events == 1)
>
> At least, It was my original intention in the code.
>
>
>
>> return (fp_ops->enqueue)(port, ev);
>> else
>> return fn(port, ev, nb_events);
>> @@ -2200,7 +2200,7 @@ rte_event_dequeue_burst(uint8_t dev_id, uint8_t port_id, struct rte_event ev[],
>> * Allow zero cost non burst mode routine invocation if application
>> * requests nb_events as const one
>> */
>> - if (nb_events == 1)
>> + if (__extension__(__builtin_constant_p(nb_events)) && nb_events == 1)
>> return (fp_ops->dequeue)(port, ev, timeout_ticks);
>> else
>> return (fp_ops->dequeue_burst)(port, ev, nb_events,
>> --
>> 2.34.1
>>
next prev parent reply other threads:[~2023-05-12 13:15 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-11 6:43 [PATCH] " Mattias Rönnblom
2023-05-11 7:09 ` Morten Brørup
2023-05-11 8:16 ` [PATCH v2] " Mattias Rönnblom
2023-05-11 8:24 ` [PATCH v3] " Mattias Rönnblom
2023-05-11 9:01 ` Morten Brørup
2023-05-12 11:59 ` Jerin Jacob
2023-05-12 13:15 ` Mattias Rönnblom [this message]
2023-05-12 13:56 ` Morten Brørup
2023-05-12 14:52 ` Mattias Rönnblom
2023-05-15 12:33 ` Jerin Jacob
2023-05-15 12:38 ` Jerin Jacob
2023-05-15 20:52 ` Mattias Rönnblom
2023-05-16 13:08 ` Jerin Jacob
2023-05-17 7:16 ` Mattias Rönnblom
2023-05-17 12:28 ` Jerin Jacob
2023-05-11 8:24 ` [PATCH v2] " Morten Brørup
2023-05-11 8:29 ` [PATCH] " Mattias Rönnblom
2023-05-11 9:06 ` Morten Brørup
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