Hello , I am working on TCP checksum offload , TSO and zero copy with linux 2.6.1 kernel . IMHO I find that the code for TCP checksum offload and TSO are already supported by the linux 2.6 kernel . I arrived at this conclusion on seeing the presence of flag CHECKSUM_HW and the #defines for NETIF_F_IP_CSUM , NETIF_F_NO_CSUM and NETIF_F_HW_CSUM . By default , it seems that CHECKSUM_HW is enabled by default so that the TSO supported driver will do the processing on the ethernet card. Please correct me if I am wrong . In the driver for e1000 and tg3 , support for TSO is already seen . But when I was testing the performance using ttcp utility , I found some weird results. I just want to share to obtain some feedback from some experienced guys in this area who has already worked in TSO ,TCP checksum offload . On the server machine I had my linux 2.6 kernel running and it had e1000 Intel pro ethercard support.Initially with ethtool utility I ensured that the Tx and Rx checksum setting on e1000 is set to on . I started ttcp utiltity in receive mode on the server machine listening on my specified port . Next I pumped in data from my client machine using ttcp utility in transmit mode to the server . I measured the time duration for data transfer to happen . say x milliseconds. Next I set the tx and rx checksum on e1000 card using ethtool , and repeated the above test with ttcp utility .Since the content size is same and with tx/rx checksum off on e1000 , I expected the time duaration of data transfer from server to client to be x+some delta . But surprisingly I am noticing the data transfer at lesser time than x .(ie faster than before with tx/rx checksum off on e1000 ) . I would appreciate if anyone could shed some light on this odd behaviour . I have pasted below what I encountered :- setup ----- aniket-linux is client m/c tc105 is server m/c which has linux 2.6.1 kernel running on it . eth2 is e1000 NIC on tc105 which supports checksum offload and segmentation offloading [root@tc105 mpm]# ethtool -k eth2 RX/TX checksumming parameters for eth2: rx-checksumming: on tx-checksumming: on scatter-gather: on [root@tc105 mpm]# Pumping data to server tc105 when rx-checksum and --------------------------------------------------- tx-checksum are enabled on the server's NIC interface ----------------------------------------------------- eth2 ----- [magesh@aniket-linux current]$ ls rpm_topdir [magesh@aniket-linux current]$ tar of - rpm_topdir | ttcp -t tc105 -p 4001 ttcp-t: buflen=8192, nbuf=2048, align=16384/0, port=4001 tcp -> tc105 ttcp-t: socket ttcp-t: connect ttcp-t: 216442880 bytes in 299.34 real seconds = 706.13 KB/sec +++ ttcp-t: 40574 I/O calls, msec/call = 7.55, calls/sec = 135.55 ttcp-t: 0.0user 2.2sys 4:59real 0% 0i+0d 0maxrss 0+2pf 0+0csw [magesh@aniket-linux current]$ [root@tc105 mpm]# ethtool -k eth2 RX/TX checksumming parameters for eth2: rx-checksumming: off tx-checksumming: off scatter-gather: on [root@tc105 mpm]# Pumping data to server tc105 when rx-checksum and --------------------------------------------------- tx-checksum are disabled on the server's NIC interface ----------------------------------------------------- eth2 ----- [magesh@aniket-linux current]$ tar cf - rpm_topdir | ttcp -t tc105 -p 4001 ttcp-t: buflen=8192, nbuf=2048, align=16384/0, port=4001 tcp -> tc105 ttcp-t: socket ttcp-t: connect ttcp-t: 216442880 bytes in 62.26 real seconds = 3394.84 KB/sec +++ ttcp-t: 36257 I/O calls, msec/call = 1.76, calls/sec = 582.33 ttcp-t: 0.1user 1.8sys 1:02real 3% 0i+0d 0maxrss 0+2pf 0+0csw [magesh@aniket-linux current]$ I would also appreciate if any one could shed more light on zero copy functionality support in linux 2.6.1 Thanks Magesh __________________________________ Do you Yahoo!? Get better spam protection with Yahoo! Mail. http://antispam.yahoo.com/tools - : send the line "unsubscribe linux-net" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
