Experiences Getting SystemTap work on OLPC Machine

[William Cohen]

Dan Williams wrote:

> You may want to update to the Q2B81 firmware which disables the branch
> prediction workaround, and yields about 25% performance increase when
> using any USB network devices (including the builtin wireless).  You
> don't have to reflash the NAND to do this, so you wouldn't need to blow
> away the setup you've already got.
> 
> dan

I updated the machine to Q2B81 firmware and reran the experiment with the 
machine being idle. The percentage of time spent in the idle looks the same. I 
do see the "percent halted" go down when I put load on the machine. The "exited 
default_halt" is lower than the "entered default_halt" in this particular data run.

-Will



# staprun idle1.ko
Starting halt watch
Ran for 647276729 us
entered default_halt 100228
exited default_halt 100204
percent halted: 17
count: 100204
avg_time: 1140
min_time: 1
max_time: 3438
usec                distribution
value |-------------------------------------------------- count
     0 |                                                       0
     1 |                                                       1
     2 |                                                     212
     4 |                                                     911
     8 |                                                    1070
    16 |@                                                   1689
    32 |                                                    1386
    64 |                                                    1392
   128 |                                                    1503
   256 |@                                                   2753
   512 |@@@                                                 5264
  1024 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@  83782
  2048 |                                                     241
  4096 |                                                       0
  8192 |                                                       0