Strange performance results -- any ideas?

[Dirk Zimoch <dirk.zimoch@psi.ch>]

Hi all,

I am testing the performance of array parsing with StreamDevice on a 
Linux system. I am reading strings like "3.1415,3.1415,...\n" into a 
waveform record with FTVL=DOUBLE. The input is via TCP from localhost.

I found a very strange duration/size relationship:
size       1     duration:      423     time/element:  423.0
size       2     duration:      234     time/element:  117.0
size       4     duration:      229     time/element:   57.2
size       8     duration:      239     time/element:   29.9
size      16     duration:      238     time/element:   14.9
size      32     duration:      259     time/element:    8.1
size      64     duration:      281     time/element:    4.4
size     128     duration:      312     time/element:    2.4
size     256     duration:      397     time/element:    1.6
size     512     duration:      552     time/element:    1.1
size    1024     duration:    40023     time/element:   39.1
size    2048     duration:    41450     time/element:   20.2
size    4096     duration:    41678     time/element:   10.2
size    8192     duration:     5579     time/element:    0.7
size   16384     duration:    10947     time/element:    0.7
size   32768     duration:    21826     time/element:    0.7
size   65536     duration:    43508     time/element:    0.7
size  131072     duration:    77358     time/element:    0.6
size  262144     duration:   138533     time/element:    0.5
size  524288     duration:   275591     time/element:    0.5
size 1048576     duration:   518404     time/element:    0.5

All times are in 1e-6 seconds. Time is measured on the server. The clock 
starts before sending the string and stops after the waveform sends back 
an acknowledge.

Protocol: {in "%f"; out "%(NORD)d";}

I understand that for small arrays, the time is dominated by overhead 
and stays more or less constant.

But does anyone have an idea why is there this strange performance drop 
for sizes between 1024 and 4096 elements?

Dirk