netdev-dpdk: Remove use of rte_mempool_ops_get_count.

rte_mempool_ops_get_count is not exported by DPDK so it means it
cannot be used by OVS when using DPDK as a shared library.

Remove rte_mempool_ops_get_count but still use rte_mempool_full
and document it's behavior.

Fixes: 91fccdad72a2 ("netdev-dpdk: Free mempool only when no in-use mbufs.")
Reported-by: Timothy Redaelli <tredaelli@redhat.com>
Reported-by: Markos Chandras <mchandras@suse.de>
Signed-off-by: Kevin Traynor <ktraynor@redhat.com>
Signed-off-by: Ian Stokes <ian.stokes@intel.com>

diff --git a/lib/netdev-dpdk.c b/lib/netdev-dpdk.c
index 52d8fe6b7ac2a06520a3a2a8278a57a0be47fbe3..397f7b121cd5d809500a4b14770f9734485e3bc1 100644 (file)
--- a/lib/netdev-dpdk.c
+++ b/lib/netdev-dpdk.c
@@ -598,19 +598,20 @@ dpdk_mp_create(int socket_id, int mtu)
 static int
 dpdk_mp_full(const struct rte_mempool *mp) OVS_REQUIRES(dpdk_mp_mutex)
 {
-    unsigned ring_count;
-    /* This logic is needed because rte_mempool_full() is not guaranteed to
-     * be atomic and mbufs could be moved from mempool cache --> mempool ring
-     * during the call. However, as no mbufs will be taken from the mempool
-     * at this time, we can work around it by also checking the ring entries
-     * separately and ensuring that they have not changed.
+    /* At this point we want to know if all the mbufs are back
+     * in the mempool. rte_mempool_full() is not atomic but it's
+     * the best available and as we are no longer requesting mbufs
+     * from the mempool, it means mbufs will not move from
+     * 'mempool ring' --> 'mempool cache'. In rte_mempool_full()
+     * the ring is counted before caches, so we won't get false
+     * positives in this use case and we handle false negatives.
+     *
+     * If future implementations of rte_mempool_full() were to change
+     * it could be possible for a false positive. Even that would
+     * likely be ok, as there are additional checks during mempool
+     * freeing but it would make things racey.
      */
-    ring_count = rte_mempool_ops_get_count(mp);
-    if (rte_mempool_full(mp) && rte_mempool_ops_get_count(mp) == ring_count) {
-        return 1;
-    }
-
-    return 0;
+    return rte_mempool_full(mp);
 }
 
 /* Free unused mempools. */