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

["Mattias Rönnblom" <hofors@lysator.liu.se>]

On 2024-04-26 10:27, Ferruh Yigit wrote:
> 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 {
> ...
> };
> ```

Right. Sorry, forgot about that.

I've made a v3 (which is actually marked v3).