distributor: add comments

Add in some additional comments around more complex areas of the code
so as to make the code easier to read and understand.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>

diff --git a/lib/librte_distributor/rte_distributor.c b/lib/librte_distributor/rte_distributor.c
index 585ff88..656ee5c 100644 (file)
--- a/lib/librte_distributor/rte_distributor.c
+++ b/lib/librte_distributor/rte_distributor.c
@@ -92,6 +92,7 @@ struct rte_distributor {
        unsigned num_workers;                 /**< Number of workers polling */
 
        uint32_t in_flight_tags[RTE_MAX_LCORE];
+               /**< Tracks the tag being processed per core, 0 == no pkt */
        struct rte_distributor_backlog backlog[RTE_MAX_LCORE];
 
        union rte_distributor_buffer bufs[RTE_MAX_LCORE];
@@ -282,10 +283,22 @@ rte_distributor_process(struct rte_distributor *d,
                        next_mb = mbufs[next_idx++];
                        next_value = (((int64_t)(uintptr_t)next_mb)
                                        << RTE_DISTRIB_FLAG_BITS);
+                       /*
+                        * Set the low bit on the tag, so we can guarantee that
+                        * we never store a tag value of zero. That means we can
+                        * use the zero-value to indicate that no packet is
+                        * being processed by a worker.
+                        */
                        new_tag = (next_mb->hash.rss | 1);
 
                        uint32_t match = 0;
                        unsigned i;
+                       /*
+                        * to scan for a match use "xor" and "not" to get a 0/1
+                        * value, then use shifting to merge to single "match"
+                        * variable, where a one-bit indicates a match for the
+                        * worker given by the bit-position
+                        */
                        for (i = 0; i < d->num_workers; i++)
                                match |= (!(d->in_flight_tags[i] ^ new_tag)
                                        << i);