em(4): Reduce EM_TXDD_SAFE from 50 to 48.

With this change, the device will have at most 48 TX descriptors pending
to be write back.  48 is chosen according to the table listed on:
Intel 82571EB/82572EI Ethernet Controller Revision 6.0, Page 43,
Item 70. 82571/82572 Overwrites Transmit Descriptors in Internal Buffer.

diff --git a/sys/dev/netif/em/if_em.h b/sys/dev/netif/em/if_em.h
index b291619..5077997 100644 (file)
--- a/sys/dev/netif/em/if_em.h
+++ b/sys/dev/netif/em/if_em.h
@@ -346,7 +346,7 @@ struct adapter {
        int                     tx_dd_tail;
        int                     tx_dd_head;
 #define EM_TXDD_MAX    64
-#define EM_TXDD_SAFE   50 /* must be less than EM_TXDD_MAX */
+#define EM_TXDD_SAFE   48 /* must be less than EM_TXDD_MAX */
        int                     tx_dd[EM_TXDD_MAX];
 
        /*