[dpdk-dev] [PATCH v2 2/2] Add in_flight_bitmask so as to use full 32 bits of tag.

[Qinglai Xiao <jigsaw@gmail.com>]

With introduction of in_flight_bitmask, the whole 32 bits of tag can be
used. Further more, this patch fixed the integer overflow when finding
the matched tags.
Note that currently librte_distributor supports up to 64 worker threads.
If more workers are needed, the size of in_flight_bitmask and the
algorithm of finding matched tag must be revised.

Signed-off-by: Qinglai Xiao <jigsaw@gmail.com>
---
 lib/librte_distributor/rte_distributor.c |   45 ++++++++++++++++++++++--------
 lib/librte_distributor/rte_distributor.h |    4 ++
 2 files changed, 37 insertions(+), 12 deletions(-)

diff --git a/lib/librte_distributor/rte_distributor.c b/lib/librte_distributor/rte_distributor.c
index 3dfec4a..3dfccae 100644
--- a/lib/librte_distributor/rte_distributor.c
+++ b/lib/librte_distributor/rte_distributor.c
@@ -92,7 +92,13 @@ 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 */
+		/**< Tracks the tag being processed per core */
+	uint64_t in_flight_bitmask;
+		/**< on/off bits for in-flight tags.
+		 * Note that if RTE_MAX_LCORE is larger than 64 then
+		 * the bitmask has to expand.
+		 */
+
 	struct rte_distributor_backlog backlog[RTE_MAX_LCORE];
 
 	union rte_distributor_buffer bufs[RTE_MAX_LCORE];
@@ -189,6 +195,7 @@ static inline void
 handle_worker_shutdown(struct rte_distributor *d, unsigned wkr)
 {
 	d->in_flight_tags[wkr] = 0;
+	d->in_flight_bitmask &= ~(1UL << wkr);
 	d->bufs[wkr].bufptr64 = 0;
 	if (unlikely(d->backlog[wkr].count != 0)) {
 		/* On return of a packet, we need to move the
@@ -211,7 +218,10 @@ handle_worker_shutdown(struct rte_distributor *d, unsigned wkr)
 			pkts[i] = (void *)((uintptr_t)(bl->pkts[idx] >>
 					RTE_DISTRIB_FLAG_BITS));
 		}
-		/* recursive call */
+		/* recursive call.
+		 * Note that the tags were set before first level call
+		 * to rte_distributor_process.
+		 */
 		rte_distributor_process(d, pkts, i);
 		bl->count = bl->start = 0;
 	}
@@ -242,6 +252,7 @@ process_returns(struct rte_distributor *d)
 			else {
 				d->bufs[wkr].bufptr64 = RTE_DISTRIB_GET_BUF;
 				d->in_flight_tags[wkr] = 0;
+				d->in_flight_bitmask &= ~(1UL << wkr);
 			}
 			oldbuf = data >> RTE_DISTRIB_FLAG_BITS;
 		} else if (data & RTE_DISTRIB_RETURN_BUF) {
@@ -284,14 +295,18 @@ rte_distributor_process(struct rte_distributor *d,
 			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.
+			 * User is advocated to set tag vaue for each
+			 * mbuf before calling rte_distributor_process.
+			 * User defined tags are used to identify flows,
+			 * or sessions.
 			 */
-			new_tag = (next_mb->hash.usr | 1);
+			new_tag = next_mb->hash.usr;
 
-			uint32_t match = 0;
+			/*
+			 * Note that if RTE_MAX_LCORE is larger than 64 then
+			 * the size of match has to be expanded.
+			 */
+			uint64_t match = 0;
 			unsigned i;
 			/*
 			 * to scan for a match use "xor" and "not" to get a 0/1
@@ -303,9 +318,12 @@ rte_distributor_process(struct rte_distributor *d,
 				match |= (!(d->in_flight_tags[i] ^ new_tag)
 					<< i);
 
+			/* Only turned-on bits are considered as match */
+			match &= d->in_flight_bitmask;
+
 			if (match) {
 				next_mb = NULL;
-				unsigned worker = __builtin_ctz(match);
+				unsigned worker = __builtin_ctzl(match);
 				if (add_to_backlog(&d->backlog[worker],
 						next_value) < 0)
 					next_idx--;
@@ -322,6 +340,7 @@ rte_distributor_process(struct rte_distributor *d,
 			else {
 				d->bufs[wkr].bufptr64 = next_value;
 				d->in_flight_tags[wkr] = new_tag;
+				d->in_flight_bitmask |= (1UL << wkr);
 				next_mb = NULL;
 			}
 			oldbuf = data >> RTE_DISTRIB_FLAG_BITS;
@@ -379,11 +398,13 @@ rte_distributor_returned_pkts(struct rte_distributor *d,
 static inline unsigned
 total_outstanding(const struct rte_distributor *d)
 {
-	unsigned wkr, total_outstanding = 0;
+	unsigned wkr, total_outstanding;
+
+	total_outstanding = __builtin_popcountl(d->in_flight_bitmask);
 
 	for (wkr = 0; wkr < d->num_workers; wkr++)
-		total_outstanding += d->backlog[wkr].count +
-				!!(d->in_flight_tags[wkr]);
+		total_outstanding += d->backlog[wkr].count;
+
 	return total_outstanding;
 }
 
diff --git a/lib/librte_distributor/rte_distributor.h b/lib/librte_distributor/rte_distributor.h
index ec0d74a..cc1d559 100644
--- a/lib/librte_distributor/rte_distributor.h
+++ b/lib/librte_distributor/rte_distributor.h
@@ -88,6 +88,10 @@ rte_distributor_create(const char *name, unsigned socket_id,
  * packets. The distributor will ensure that no two packets that have the
  * same flow id, or tag, in the mbuf will be procesed at the same time.
  *
+ * The user is advocated to set tag for each mbuf before calling this function.
+ * If user doesn't set the tag, the tag value can be various values depending on
+ * driver implementation and configuration.
+ *
  * This is not multi-thread safe and should only be called on a single lcore.
  *
  * @param d
-- 
1.7.1