DPDK 20.11 compilation and testing with clang 5.0.0 compiler - reg.

DPDK 20.11 compilation and testing with clang 5.0.0 compiler - reg.

[Sundararaman Rajagopalan]

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Hi Team,

We are trying to compile and run dpdk 20.11 pipeline using clang (LLVM 5.0) compiler. We are able to compile and run the pipeline. However, we observed a lot of pkts not executing the acl lookup properly. While debugging, we found that a lot of pkts were missed in packets out mask. This aspect was checked with the rte_table_acl_lookup function in lib/librte_table/rte_table_acl.c file.

Here is the function:

static int
rte_table_acl_lookup(
    void *table,
    struct rte_mbuf **pkts,
    uint64_t pkts_mask,
    uint64_t *lookup_hit_mask,
    void **entries)
{
    struct rte_table_acl *acl = (struct rte_table_acl *) table;
    const uint8_t *pkts_data[RTE_PORT_IN_BURST_SIZE_MAX];
    uint32_t results[RTE_PORT_IN_BURST_SIZE_MAX];
    uint64_t pkts_out_mask;
    uint32_t n_pkts, i, j;

     __rte_unused uint32_t n_pkts_in = __builtin_popcountll(pkts_mask);
    RTE_TABLE_ACL_STATS_PKTS_IN_ADD(acl, n_pkts_in);

     /* Input conversion */
    for (i = 0, j = 0; i < (uint32_t)(RTE_PORT_IN_BURST_SIZE_MAX -
        __builtin_clzll(pkts_mask)); i++) {
        uint64_t pkt_mask = 1LLU << i;

         if (pkt_mask & pkts_mask) {
            pkts_data[j] = rte_pktmbuf_mtod(pkts[i], uint8_t *);
            j++;
        }
    }
    n_pkts = j;


    /* Low-level ACL table lookup */
    if (acl->ctx != NULL)
        rte_acl_classify(acl->ctx, pkts_data, results, n_pkts, 1);
    else
        n_pkts = 0;


    /* Output conversion */
    pkts_out_mask = 0;
    for (i = 0; i < n_pkts; i++) {
        uint32_t action_table_pos = results[i];
        uint32_t pkt_pos = __builtin_ctzll(pkts_mask);
        uint64_t pkt_mask = 1LLU << pkt_pos;

         pkts_mask &= ~pkt_mask;

         if (action_table_pos != 0) {
            pkts_out_mask |= pkt_mask;
            entries[pkt_pos] = (void *)
&acl->memory[action_table_pos *
                acl->entry_size];
            rte_prefetch0(entries[pkt_pos]);
        }
    }

     *lookup_hit_mask = pkts_out_mask;
    RTE_TABLE_ACL_STATS_PKTS_LOOKUP_MISS(acl, n_pkts_in - __builtin_popcountll(pkts_out_mask));

     return 0;
}

Can you provide some suggestions to avoid this issue and enable acl to run without functionality loss?

Thanks and regards,

R. Sundararaman

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Re: DPDK 20.11 compilation and testing with clang 5.0.0 compiler - reg.

[Stephen Hemminger]

On Thu, 13 Apr 2023 11:32:25 +0000
Sundararaman Rajagopalan <Sundararaman.Rajagopalan@tatacommunications.com> wrote:

> Hi Team,
> 
> We are trying to compile and run dpdk 20.11 pipeline using clang (LLVM 5.0) compiler. We are able to compile and run the pipeline. However, we observed a lot of pkts not executing the acl lookup properly. While debugging, we found that a lot of pkts were missed in packets out mask. This aspect was checked with the rte_table_acl_lookup function in lib/librte_table/rte_table_acl.c file.

Clang 5 is from September 2017
Leading edge Linux distributions are using Clang 14 from March 2022
Current release is Clang 16.

Does your problem reproduce on current compiler? Or if built with Gcc