MFC: 279094

sfxge: more accurate calculation of maximum number of TSO segments

Sponsored by:   Solarflare Communications, Inc.
Approved by:    gnn (mentor)

2 files changed, 14 insertions, 4 deletions

diff --git a/sys/dev/sfxge/sfxge_tx.c b/sys/dev/sfxge/sfxge_tx.c
index c1e09a4..63dd8d7 100644
--- a/sys/dev/sfxge/sfxge_tx.c
+++ b/sys/dev/sfxge/sfxge_tx.c
@@ -72,10 +72,10 @@ __FBSDID("$FreeBSD$");
  * maximum mbuf length we might need more than a ring-ful of
  * descriptors, but this should not happen in practice except
  * due to deliberate attack.  In that case we will truncate
- * the output at a packet boundary.  Allow for a reasonable
- * minimum MSS of 512.
+ * the output at a packet boundary.
  */
-#define	SFXGE_TSO_MAX_DESC ((65535 / 512) * 2 + SFXGE_TX_MAPPING_MAX_SEG - 1)
+#define	SFXGE_TSO_MAX_DESC						\
+	(SFXGE_TSO_MAX_SEGS * 2 + SFXGE_TX_MAPPING_MAX_SEG - 1)
 #define	SFXGE_TXQ_BLOCK_LEVEL(_entries)	((_entries) - SFXGE_TSO_MAX_DESC)
 
 #ifdef SFXGE_HAVE_MQ
diff --git a/sys/dev/sfxge/sfxge_tx.h b/sys/dev/sfxge/sfxge_tx.h
index b430288..3965ffd 100644
--- a/sys/dev/sfxge/sfxge_tx.h
+++ b/sys/dev/sfxge/sfxge_tx.h
@@ -36,12 +36,22 @@
 #include <netinet/ip.h>
 #include <netinet/tcp.h>
 
+/* Maximum size of TSO packet */
+#define	SFXGE_TSO_MAX_SIZE		(65535)
+
+/*
+ * Maximum number of segments to be created for a TSO packet.
+ * Allow for a reasonable minimum MSS of 512.
+ */
+#define	SFXGE_TSO_MAX_SEGS		howmany(SFXGE_TSO_MAX_SIZE, 512)
+
 /* Maximum number of DMA segments needed to map an mbuf chain.  With
  * TSO, the mbuf length may be just over 64K, divided into 2K mbuf
  * clusters.  (The chain could be longer than this initially, but can
  * be shortened with m_collapse().)
  */
-#define	SFXGE_TX_MAPPING_MAX_SEG	(64 / 2 + 1)
+#define	SFXGE_TX_MAPPING_MAX_SEG					\
+	(1 + howmany(SFXGE_TSO_MAX_SIZE, MCLBYTES))
 
 /*
  * Buffer mapping flags.