Re: [PATCH] net/af_packet: cache align Rx/Tx structs

[Ferruh Yigit <ferruh.yigit@amd.com>]

On 4/26/2024 8:38 AM, Mattias Rönnblom wrote:
> Cache align Rx and Tx queue struct to avoid false sharing.
> 
> RX struct happens to be 64 bytes on x86_64 already, so cache alignment
> has no effect there, but it does on 32-bit ISAs.
> 
> TX struct is 56 bytes on x86_64.
> 
> Both structs keep counters, and in the RX case they are updated even
> for empty polls.
> 
> Fixes: 364e08f2bbc0 ("af_packet: add PMD for AF_PACKET-based virtual devices")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
> ---
>  drivers/net/af_packet/rte_eth_af_packet.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/af_packet/rte_eth_af_packet.c b/drivers/net/af_packet/rte_eth_af_packet.c
> index 397a32db58..28aeb7d08e 100644
> --- a/drivers/net/af_packet/rte_eth_af_packet.c
> +++ b/drivers/net/af_packet/rte_eth_af_packet.c
> @@ -6,6 +6,7 @@
>   * All rights reserved.
>   */
>  
> +#include <rte_common.h>
>  #include <rte_string_fns.h>
>  #include <rte_mbuf.h>
>  #include <ethdev_driver.h>
> @@ -53,7 +54,7 @@ struct pkt_rx_queue {
>  
>  	volatile unsigned long rx_pkts;
>  	volatile unsigned long rx_bytes;
> -};
> +} __rte_cache_aligned;
>  
>  struct pkt_tx_queue {
>  	int sockfd;
> @@ -67,7 +68,7 @@ struct pkt_tx_queue {
>  	volatile unsigned long tx_pkts;
>  	volatile unsigned long err_pkts;
>  	volatile unsigned long tx_bytes;
> -};
> +} __rte_cache_aligned;
>  
>  struct pmd_internals {
>  	unsigned nb_queues;

Hi Mattias,

I guess my comment missed, location of '__rte_cache_aligned' tag changed
for MSVC support, it should be like:
```
struct __rte_cache_aligned pkt_rx_queue {
...
};
```