Re: [dpdk-dev] [EXT] [PATCH v2 2/4] trace: remove size limit on CTF event description

[David Marchand]

On Thu, Oct 29, 2020 at 10:36 AM Sunil Kumar Kori <sk...@marvell.com> wrote:
> Yes but I am not able to understand that how tp->ctf_field will be populated 
> with latest memory
> because RTE_PER_LCORE(ctf_field) is being free and re-allocated at runtime.

Initially, RTE_PER_LCORE(ctf_field) is NULL.

Then registration for a trace point happens:

__rte_trace_point_register() calls register_fn() which for each field
in the trace point calls __rte_trace_point_emit_field().

Each call to __rte_trace_point_emit_field accumulates the previous
ctf_field with the new field.

        rc = asprintf(&field, "%s        %s %s;\n",
                RTE_PER_LCORE(ctf_field) != NULL ?
                        RTE_PER_LCORE(ctf_field) : "",
                datatype, in);
        free(RTE_PER_LCORE(ctf_field));
        RTE_PER_LCORE(ctf_field) = field;

Here, RTE_PER_LCORE(ctf_field) is != NULL.

Back to __rte_trace_point_register:

        /* Copy the accumulated fields description and clear it for the next
         * trace point.
         */
        tp->ctf_field = RTE_PER_LCORE(ctf_field);

Once stored, RTE_PER_LCORE(ctf_field) is cleared again for the next
trace point registration.

        RTE_PER_LCORE(ctf_field) = NULL;



-- 
David Marchand