> How much improvement have you measured?

with p3 700 + fxp + xen domain0 + nttcp,

sosend_loan_bonus = 0:

kaeru% time nttcp -T -n10240 bear                                           [~]
     Bytes  Real s   CPU s Real-MBit/s  CPU-MBit/s   Calls  Real-C/s   CPU-C/s
l 41943040    3.56    0.97     94.1769    346.5400   10240   2874.05   10575.6
1 41943040    3.57    0.89     94.1093    378.3586   28552   8007.91   32195.1
nttcp -T -n10240 bear  0.00s user 0.98s system 27% cpu 3.608 total

sosend_loan_bonus = 4096:

kaeru% time nttcp -T -n10240 bear                                           [~]
     Bytes  Real s   CPU s Real-MBit/s  CPU-MBit/s   Calls  Real-C/s   CPU-C/s
l 41943040    3.56    0.79     94.1826    426.2509   10240   2874.22   13008.1
1 41943040    3.57    0.88     94.1091    379.6442   28604   8022.48   32363.4
nttcp -T -n10240 bear  0.01s user 0.79s system 22% cpu 3.608 total

YAMAMOTO Takashi