svn commit: r271946 - in head/sys: dev/oce dev/vmware/vmxnet3 dev/xen/netfront kern net netinet ofed/drivers/net/mlx4 sys

Roger Pau Monné royger at FreeBSD.org
Tue Sep 15 08:32:23 UTC 2015


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?

FWIW, just using r287775 seems to solve the problem, even if I leave
if_hw_tsomax with it's current value.

Roger.



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