[PATCH 2/6] sfxge: limit software Tx queue size

[Andrew Rybchenko]

sfxge: limit software Tx queue size

Previous implementation limits put queue size only (when Tx lock can't 
be acquired),
but get queue may grow unboundedly which results in mbuf pools 
exhaustion and
latency growth.

Submitted-by:   Andrew Rybchenko <Andrew.Rybchenko at oktetlabs.ru>
Sponsored by:   Solarflare Communications, Inc.

diff -r ff9f5d3dbafe -r 7632a3355224 src/driver/freebsd/sfxge_tx.c
--- a/head/sys/dev/sfxge/sfxge_tx.c    Tue Mar 04 13:15:13 2014 +0400
+++ b/head/sys/dev/sfxge/sfxge_tx.c    Wed Mar 05 09:06:01 2014 +0400
@@ -461,6 +461,9 @@

          sfxge_tx_qdpl_swizzle(txq);

+        if (stdp->std_count >= SFXGE_TX_DPL_GET_PKT_LIMIT_DEFAULT)
+            return ENOBUFS;
+
          *(stdp->std_getp) = mbuf;
          stdp->std_getp = &mbuf->m_nextpkt;
          stdp->std_count++;
@@ -480,7 +483,7 @@
                  old_len = mp->m_pkthdr.csum_data;
              } else
                  old_len = 0;
-            if (old_len >= SFXGE_TX_MAX_DEFERRED)
+            if (old_len >= SFXGE_TX_DPL_PUT_PKT_LIMIT_DEFAULT)
                  return ENOBUFS;
              mbuf->m_pkthdr.csum_data = old_len + 1;
              mbuf->m_nextpkt = (void *)old;
@@ -507,12 +510,9 @@
       */
      locked = mtx_trylock(&txq->lock);

-    /*
-     * Can only fail if we weren't able to get the lock.
-     */
      if (sfxge_tx_qdpl_put(txq, m, locked) != 0) {
-        KASSERT(!locked,
-            ("sfxge_tx_qdpl_put() failed locked"));
+        if (locked)
+            mtx_unlock(&txq->lock);
          rc = ENOBUFS;
          goto fail;
      }
diff -r ff9f5d3dbafe -r 7632a3355224 src/driver/freebsd/sfxge_tx.h
--- a/head/sys/dev/sfxge/sfxge_tx.h    Tue Mar 04 13:15:13 2014 +0400
+++ b/head/sys/dev/sfxge/sfxge_tx.h    Wed Mar 05 09:06:01 2014 +0400
@@ -75,7 +75,8 @@
      enum sfxge_tx_buf_flags    flags;
  };

-#define SFXGE_TX_MAX_DEFERRED 64
+#define SFXGE_TX_DPL_GET_PKT_LIMIT_DEFAULT    64
+#define SFXGE_TX_DPL_PUT_PKT_LIMIT_DEFAULT    64

  /*
   * Deferred packet list.