From 5bd3f1337e94b744dfde90346c2304d0b558ea8e Mon Sep 17 00:00:00 2001 From: rmacklem Date: Tue, 6 May 2014 02:54:59 +0000 Subject: 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. --- sys/net/if.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/sys/net/if.c b/sys/net/if.c index 0356ec7..ea2aa85 100644 --- a/sys/net/if.c +++ b/sys/net/if.c @@ -74,6 +74,7 @@ #include #if defined(INET) || defined(INET6) +#include #include #include #include @@ -658,7 +659,8 @@ if_attach_internal(struct ifnet *ifp, int vmove) #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__)); -- cgit v1.1