RE: rss calculation as the nic

[Ori Kam <orika@nvidia.com>]

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Hi Yaron,

I can see some possible issues with your code, please see below.

From: Yaron Illouz <yaroni@radcom.com>
Sent: Saturday, February 3, 2024 7:03 PM
To: dev@dpdk.org; 'users@dpdk.org' <users@dpdk.org>
Subject: rss calculation as the nic

[Snip]

static inline uint32_t
do_softrss(struct rte_mbuf *m)
{
    uint32_t input_len;
    struct rte_ipv4_tuple ipv4_tuple;

    char * pRawPacket = static_cast<char*>(rte_pktmbuf_mtod(pi_mbuf, void* ));
    IpHeader * pIpHeader = (IpHeader *)(pRawPacket + offsetOfIp);
    if(pIpHeader->GetVersion()==4)
    {
        ipv4_tuple.src_addr = rte_be_to_cpu_32(pIpHeader->dwSrcAddressBigEndian);
        ipv4_tuple.dst_addr = rte_be_to_cpu_32(pIpHeader->dwDstAddressBigEndian);
[Ori] here you are converting BE to CPU
        ipv4_tuple.sport = *(uint16_t*)(pRawPacket + transportLayerOffset);
        ipv4_tuple.dport = *(uint16_t*)(pRawPacket + transportLayerOffset+2);
[Ori] here you keep the values as BE
        input_len = RTE_THASH_V4_L3_LEN;
        return rte_softrss_be((uint32_t *)&ipv4_tuple, input_len, rss_key_be);
[Ori] the above function expects to get everything in BE and  you should also call rte_convert_rss_key before the use of the above function.
    }
    return 0;
}
new_rss = do_softrss(mbuf_pointer);
std::cout<< std::hex << mbuf_pointer->hash.rss << " -> " << new_rss << std::dec << std::endl;

And i get a different value than the mbuf_pointer->hash.rss
5ed28a5c -> 33eb33eb
974c1896 -> 24e224e2
1edf1638 -> 21752175
8a54c19 -> 80638063
459a6f76 -> 1b351b35
1cdf1d1c -> e53be53b


****  I understand it is possible to do it, but i don't get the same value  ***
ethtool -i ens5f0
driver: mlx5_core
version: 5.8-3.0.7
firmware-version: 22.32.2004 (MT_0000000437)
expansion-rom-version:
bus-info: 0000:83:00.0
supports-statistics: yes
supports-test: yes
supports-eeprom-access: no
supports-register-dump: no
supports-priv-flags: yes


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