Author: rmacklem
Date: Tue May 6 02:54:59 2014
New Revision: 265414
URL: http://svnweb.freebsd.org/changeset/base/265414
Log:
MFC: r264630
For NFS mounts using rsize,wsize=65536 over TSO enabled
network interfaces limited to 32 transmit segments, there
are two known issues.
The more serious one is that for an I/O of slightly less than 64K,
the net device driver prepends an ethernet header, resulting in a
TSO segment slightly larger than 64K. Since m_defrag() copies this
into 33 mbuf clusters, the transmit fails with EFBIG.
A tester indicated observing a similar failure using iSCSI.
The second less critical problem is that the network
device driver must copy the mbuf chain via m_defrag()
(m_collapse() is not sufficient), resulting in measurable overhead.
This patch reduces the default size of if_hw_tsomax
slightly, so that the first issue is avoided.
Fixing the second issue will require a way for the
network device driver to inform tcp_output() that it
is limited to 32 transmit segments.
Modified:
stable/10/sys/net/if.c
Directory Properties:
stable/10/ (props changed)
Modified: stable/10/sys/net/if.c
==============================================================================
--- stable/10/sys/net/if.c Tue May 6 02:49:31 2014 (r265413)
+++ stable/10/sys/net/if.c Tue May 6 02:54:59 2014 (r265414)
@@ -74,6 +74,7 @@
#include <net/vnet.h>
#if defined(INET) || defined(INET6)
+#include <net/ethernet.h>
#include <netinet/in.h>
#include <netinet/in_var.h>
#include <netinet/ip.h>
@@ -658,7 +659,8 @@ if_attach_internal(struct ifnet *ifp, in
#if defined(INET) || defined(INET6)
/* Initialize to max value. */
if (ifp->if_hw_tsomax == 0)
- ifp->if_hw_tsomax = IP_MAXPACKET;
+ ifp->if_hw_tsomax = min(IP_MAXPACKET, 32 * MCLBYTES -
+ (ETHER_HDR_LEN + ETHER_VLAN_ENCAP_LEN));
KASSERT(ifp->if_hw_tsomax <= IP_MAXPACKET &&
ifp->if_hw_tsomax >= IP_MAXPACKET / 8,
("%s: tsomax outside of range", __func__));
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