On 2024-04-06 17:28, Morten Brørup wrote:
From: Tyler Retzlaff [mailto:roret...@linux.microsoft.com]
Sent: Thursday, 4 April 2024 19.15
RFC sample illustrating simple conversion of VLA to alloca().
Signed-off-by: Tyler Retzlaff <roret...@linux.microsoft.com>
---
[...]
--- a/lib/latencystats/rte_latencystats.c
+++ b/lib/latencystats/rte_latencystats.c
@@ -159,7 +159,7 @@ struct latency_stats_nameoff {
{
unsigned int i, cnt = 0;
uint64_t now;
- float latency[nb_pkts];
+ float *latency = alloca(sizeof(float) * nb_pkts);
In cases where we are processing packet bursts, I would prefer introducing a
global #define RTE_MAX_PKT_BURST_SIZE, indicating the max packet burst size
supported by libraries and drivers.
First question: what is meant by a "packet" here? An mbuf? A
network-layer PDU? Something that in some way relates to zero or more
packets, like an rte_event? Or just any object that are sent or receive
of some DPDK API in batches or bursts?
Second question: is RTE_MAX_PKT_BURST_SIZE meant as an upper bound, so
no API can consumer or produce a burst larger than this, it does all
APIs literally have to support that burst size.
Third question: why not just keep VLAs?
For reference, rte_config.h already has #define RTE_GRAPH_BURST_SIZE 256.
Such a common define should also be used by functions such as
rte_pktmbuf_free_bulk(); although it also supports segmented packets, so it
must still be able to handle more mbufs.
https://elixir.bootlin.com/dpdk/v24.03/source/lib/mbuf/rte_mbuf.c#L486
