From: "Morten Brørup" <mb@smartsharesystems.com>
To: "Tyler Retzlaff" <roretzla@linux.microsoft.com>, <dev@dpdk.org>
Cc: "Bruce Richardson" <bruce.richardson@intel.com>,
"Stephen Hemminger" <stephen@networkplumber.org>,
"Thomas Monjalon" <thomas@monjalon.net>
Subject: RE: [PATCH 4/4] dispatcher: use alloca instead of vla multi dimensional
Date: Sat, 6 Apr 2024 17:49:11 +0200 [thread overview]
Message-ID: <98CBD80474FA8B44BF855DF32C47DC35E9F374@smartserver.smartshare.dk> (raw)
In-Reply-To: <1712250913-1977-5-git-send-email-roretzla@linux.microsoft.com>
> From: Tyler Retzlaff [mailto:roretzla@linux.microsoft.com]
> Sent: Thursday, 4 April 2024 19.15
>
> RFC sample illustrating conversion of multi-dimensional VLA to use
> alloca().
>
> Signed-off-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
> ---
> lib/dispatcher/rte_dispatcher.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/lib/dispatcher/rte_dispatcher.c
> b/lib/dispatcher/rte_dispatcher.c
> index 7934917..f154c26 100644
> --- a/lib/dispatcher/rte_dispatcher.c
> +++ b/lib/dispatcher/rte_dispatcher.c
> @@ -119,7 +119,7 @@ struct rte_dispatcher {
> struct rte_event *events, uint16_t num_events)
> {
> int i;
> - struct rte_event bursts[EVD_MAX_HANDLERS][num_events];
> + struct rte_event *bursts = alloca(sizeof(struct rte_event) *
> EVD_MAX_HANDLERS * num_events);
This is an interesting example, because keeping the allocated memory tight probably has better cache performance than a max sized multi dimensional array, such as bursts[EVD_MAX_HANDLERS][RTE_MAX_EVENT_BURST_SIZE].
And multiplication on modern CPUs are not much slower than left shifting, as they were on CPUs ages ago.
So this suggested solution for multi dimensional arrays seems preferable.
> uint16_t burst_lens[EVD_MAX_HANDLERS] = { 0 };
> uint16_t drop_count = 0;
> uint16_t dispatch_count;
> @@ -136,7 +136,7 @@ struct rte_dispatcher {
> continue;
> }
>
> - bursts[handler_idx][burst_lens[handler_idx]] = *event;
> + bursts[handler_idx * num_events + burst_lens[handler_idx]]
> = *event;
> burst_lens[handler_idx]++;
> }
>
> @@ -152,7 +152,7 @@ struct rte_dispatcher {
> continue;
>
> handler->process_fun(dispatcher->event_dev_id, port-
> >port_id,
> - bursts[i], len, handler->process_data);
> + &bursts[i * num_events], len, handler-
> >process_data);
>
> dispatched += len;
>
> --
> 1.8.3.1
next prev parent reply other threads:[~2024-04-06 15:49 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-07 19:32 RFC acceptable handling of VLAs across toolchains Tyler Retzlaff
2023-11-08 2:31 ` Stephen Hemminger
2023-11-08 3:25 ` Tyler Retzlaff
2023-11-08 8:19 ` Morten Brørup
2023-11-08 16:51 ` Stephen Hemminger
2023-11-08 17:48 ` Morten Brørup
2023-11-09 10:25 ` RFC: default burst sizes in rte_config Morten Brørup
2023-11-09 20:26 ` RFC acceptable handling of VLAs across toolchains Tyler Retzlaff
2024-03-21 0:12 ` Tyler Retzlaff
2024-04-04 17:15 ` [PATCH 0/4] RFC samples converting VLA to alloca Tyler Retzlaff
2024-04-04 17:15 ` [PATCH 1/4] latencystats: use alloca instead of vla trivial Tyler Retzlaff
2024-04-06 15:28 ` Morten Brørup
2024-04-07 9:36 ` Mattias Rönnblom
2024-04-07 17:00 ` Stephen Hemminger
2024-04-04 17:15 ` [PATCH 2/4] hash: " Tyler Retzlaff
2024-04-06 16:01 ` Morten Brørup
2024-04-04 17:15 ` [PATCH 3/4] vhost: use alloca instead of vla sizeof Tyler Retzlaff
2024-04-06 22:30 ` Morten Brørup
2024-04-04 17:15 ` [PATCH 4/4] dispatcher: use alloca instead of vla multi dimensional Tyler Retzlaff
2024-04-06 15:49 ` Morten Brørup [this message]
2024-04-07 9:31 ` [PATCH 0/4] RFC samples converting VLA to alloca Mattias Rönnblom
2024-04-07 11:07 ` Morten Brørup
2024-04-07 17:03 ` Stephen Hemminger
2024-04-08 15:27 ` Tyler Retzlaff
2024-04-08 15:53 ` Morten Brørup
2024-04-09 8:28 ` Konstantin Ananyev
2024-04-09 15:08 ` Tyler Retzlaff
2024-04-10 9:58 ` Konstantin Ananyev
2024-04-10 17:03 ` Tyler Retzlaff
2024-04-10 7:32 ` Mattias Rönnblom
2024-04-10 7:52 ` Morten Brørup
2024-04-10 17:04 ` Tyler Retzlaff
2024-04-10 7:27 ` Mattias Rönnblom
2024-04-10 17:10 ` Tyler Retzlaff
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