El 14/09/15 a les 11.29, Hans Petter Selasky ha escrit: > On 09/14/15 11:17, Roger Pau Monné wrote: >> El 22/09/14 a les 10.27, Hans Petter Selasky ha escrit: >>> Author: hselasky >>> Date: Mon Sep 22 08:27:27 2014 >>> New Revision: 271946 >>> URL: http://svnweb.freebsd.org/changeset/base/271946 >>> >>> Log: >>> Improve transmit sending offload, TSO, algorithm in general. >>> >>> The current TSO limitation feature only takes the total number of >>> bytes in an mbuf chain into account and does not limit by the number >>> of mbufs in a chain. Some kinds of hardware is limited by two >>> factors. One is the fragment length and the second is the fragment >>> count. Both of these limits need to be taken into account when doing >>> TSO. Else some kinds of hardware might have to drop completely valid >>> mbuf chains because they cannot loaded into the given hardware's DMA >>> engine. The new way of doing TSO limitation has been made backwards >>> compatible as input from other FreeBSD developers and will use >>> defaults for values not set. >>> >>> Reviewed by: adrian, rmacklem >>> Sponsored by: Mellanox Technologies >> >> This commit makes xen-netfront tx performance drop from ~5Gbits/sec >> (with debug options enabled) to 446 Mbits/sec. I'm currently looking, >> but if anyone has ideas they are welcome. >> > > Hi Roger, > > Looking at the netfront code you should subtract 1 from tsomaxsegcount > prior to r287775. The reason might simply be that 2K clusters are used > instead of 4K clusters, causing m_defrag() to be called. > >> ifp->if_hw_tsomax = 65536 - (ETHER_HDR_LEN + >> ETHER_VLAN_ENCAP_LEN); >> ifp->if_hw_tsomaxsegcount = MAX_TX_REQ_FRAGS; >> ifp->if_hw_tsomaxsegsize = PAGE_SIZE; > > After r287775 can you try these settings: > > ifp->if_hw_tsomax = 65536; > ifp->if_hw_tsomaxsegcount = MAX_TX_REQ_FRAGS; > ifp->if_hw_tsomaxsegsize = PAGE_SIZE; > > And see if the performance is the same like before?
Yes, performance seems to be fine after setting if_hw_tsomax to 65536. Is there some documentation about the usage of if_hw_tsomax? Does the network subsystem already takes care of subtracting the space for ether header and the vlan encapsulation, so it's no longer needed to specify them in if_hw_tsomax? Also, this commit was MFC'ed to stable/10 and 10.2 suffers from the same problem. Can we issue and EN to get this fixed in 10.2? Roger. _______________________________________________ [email protected] mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "[email protected]"
