Experiences Getting SystemTap work on OLPC Machine

[Dan Williams]

On Mon, 2007-03-19 at 19:03 -0400, William Cohen wrote:
> William Cohen wrote:
> 
> > This particular script attempts to determine the amount of the time
> > spent in the power saving halted mode. It will run until control-c is
> > typed on the command line. When control-c is pressed, the script
> > prints out information about how long it ran, the number of entries
> > and exits from halt state, and some statistics about the time spent in
> > halted state. Below is the output of idle1.stp running on a idle
> > machine running the 314 build and the q2b76 rom:
> > 
> > Starting halt watch
> > Ran for 60544934 us
> > entered default_halt 9609
> > exited default_halt 9609
> > percent halted: 17
> > count: 9609
> > avg_time: 1081
> > min_time: 3
> > max_time: 3429
> > usec                distribution
> > value |-------------------------------------------------- count
> >     0 |                                                      0
> >     1 |                                                      0
> >     2 |                                                     18
> >     4 |@                                                   219
> >     8 |@                                                   295
> >    16 |                                                     56
> >    32 |@                                                   279
> >    64 |                                                    149
> >   128 |                                                    147
> >   256 |@                                                   275
> >   512 |@@@                                                 542
> >  1024 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@  7605
> >  2048 |                                                     24
> >  4096 |                                                      0
> >  8192 |                                                      0
> > 
> > This data show that the script was run for about 1 minute
> > (60,544,934us).  There were about 9600 halt entries and exits. The
> > time actually spent halted is surprisingly small, 17% for the unloaded
> > machine. The average time spent halted is slightly over
> > 1millisecond. One can see the distribution on the histogram.
> 
> Hi All,
> 
> There may be more interrupts on this system than a stock system. There were a 
> couple additions to the stock hardware:
> 
> -Linksys USB200M usb to ethernet adapter
> -4GB USB flash as root file system
> 	Memorex  Mini TravelDrive 6.51 PQ: 0 ANSI: 0 CCS

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