OK,its always good to start with facts on the ground... before
commiting this test, my original thinking was that for messages
whose size=X is less then the IB Link level MTU it holds that:
latency(X,UD) <= latency(X,UC) <= latency(X,RC)
Running the latency test provided with the perftest package on my systems (*)
I get the below results. Does anyone has insight why the --minimal-- and typical
UD latency is 1us ( = 20%) worse then the --minimal-- and typical RC latency???
Or.
(*) the system spec is:
HW : 4 way Intel Xeon 1.6GHz 4GB RAM
IB HW: Arbel memfull (25208) DDR running in SDR mode
HCA FW: 4.8.200
IB SW: OFED 1.2
OS : RH4 U3 i386 smp
[EMAIL PROTECTED] ~]# /usr/bin/ib_send_lat -c RC -n 100000 172.30.8.61
------------------------------------------------------------------
Send Latency Test
Inline data is used up to 400 bytes message
Connection type : RC
local address: LID 0x26 QPN 0x330407 PSN 0xf6ba57
remote address: LID 0x28 QPN 0x40407 PSN 0xc2c9f9
Mtu : 2048
------------------------------------------------------------------
#bytes #iterations t_min[usec] t_max[usec] t_typical[usec]
2 100000 4.75 38.53 4.82
------------------------------------------------------------------
[EMAIL PROTECTED] ~]# /usr/bin/ib_send_lat -c UC -n 100000 172.30.8.61
------------------------------------------------------------------
Send Latency Test
Inline data is used up to 400 bytes message
Connection type : UC
local address: LID 0x26 QPN 0x340407 PSN 0xbb4a0e
remote address: LID 0x28 QPN 0x50407 PSN 0xb916a9
Mtu : 2048
------------------------------------------------------------------
#bytes #iterations t_min[usec] t_max[usec] t_typical[usec]
2 100000 4.71 42.03 4.77
------------------------------------------------------------------
[EMAIL PROTECTED] ~]# /usr/bin/ib_send_lat -c UD -n 100000 172.30.8.61
------------------------------------------------------------------
Send Latency Test
Inline data is used up to 400 bytes message
Connection type : UD
local address: LID 0x26 QPN 0x350407 PSN 0xfdc2c0
remote address: LID 0x28 QPN 0x60407 PSN 0x63c30e
------------------------------------------------------------------
#bytes #iterations t_min[usec] t_max[usec] t_typical[usec]
2 100000 5.71 44.51 5.81
------------------------------------------------------------------
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