Experiences Getting SystemTap work on OLPC Machine Right now the stock Systemtap does not allow cross compiling of systemtap scripts between different subarchitectures. The stock systemtap assumes that the host and target systems are the same subarchitecture. If the host systemtap is a i686 machine and the target system is a i586 (olpc machine), the generated kernel module for the target system has runtime test that determines the module was built on a different architecture and the systemtap instrumentation module will fail when trying to initialize the module. Chris Ball made a hack that disables the runtime test. There is a systemtap bugzilla entry that describes the problem in more detail:
http://sources.redhat.com/bugzilla/show_bug.cgi?id=4186 Setup of SystemTap on Host Machine The existing systemtap-0.5.12-1.fc6 was modified to include the translate.diff patch in the systemtap bugzilla. This is a very temporary solution to work around the existing runtime architecture check. There is no way that this patch will be included in the upstream systemtap; unsupported instructions may be compiled into the target code. The systemtap rpm including the translate.diff patch was built locally on an FC6 machine with: rpmbuild -ba systemtap.spec --define "fedora 6" --define "dist olpc" Once built the systemtap and systemtap-runtime rpms were installed on the host system with: rpm -ivh systemtap-0.5.12-1olpc.i386.rpm \ systemtap-runtime-0.5.12-1olpc.i386.rpm The host machine needs the files to map the probe points to kernel executables and the host machines to be able to build modules for the target (olpc machine) kernel. The kernel rpms for the olpc machine are installed on the host machine: rpm -ivh kernel-debuginfo-2.6.21-20070312.1.olpc.3eca75102a57502.i586.rpm \ kernel-debuginfo-common-2.6.21-20070312.1.olpc.3eca75102a57502.i586.rpm \ kernel-devel-2.6.21-20070312.1.olpc.3eca75102a57502.i586.rpm \ kernel-2.6.21-20070319.olpc1p.3eca75102a57502.i586.rpm You will need to adjust the /boot/grub/grub.conf to boot the correct kernel. The installation of the kernel will assume that you will want to boot the olpc kernel. At this point modules for the olpc machine can be built on the host machine with something like the following command: stap -r 2.6.21-20070319.olpc1p.3eca75102a57502 -k idle1.stp -m idle1 The "-r 2.6.21-20070319.olpc1p.3eca75102a57502" indicates that the modules should be used to instrument the kernel for the olpc rather than the kernel currently running on the host system. The "-k" idicates that the resulting temporary files should be kept after systemtap is complete; systemtap normally erases the temporary files. The "-m idle1" renames the resulting module as "idle1.ko". Systemtap prints a line listing the directory holding the temporary data and it looks like the following: Keeping temporary directory "/tmp/stapXYktsn" The "/tmp/stapXYktsn/idle1.ko" kernel module can be copied over to the olpc machine. Setup of SystemTap on OLPC Machine To run systemtap kernel modules on olpc machine the hacked systemtap-runtime module needs to be installed on the olpc machine: rpm -Uvh systemtap-runtime-0.5.12-1olpc.i386.rpm The instrumentation needs to be run as root with: staprun idle1.ko 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. The idle1.stp script is a quick and dirty script to look at time spent in halted state. It won't work on SMP kernels, it has a line based probe that is fail if the process.c file changes, and doesn't work for kernels that use alternative idle functions. The script idle1.stp is below: # idle1.stp # This is a simple script to determine how much time is spent with the # processor actually in the halted mode. # FIXME the following will NOT work for SMP kernel with multiple processors # It does not keep track of data by a per processor basis global entries_halt global entries_halt_t global exits_halt global halt_state global start_wall_time global stats_halt probe begin { printf("Starting halt watch\n"); start_wall_time = gettimeofday_us(); } #FIXME The following should not probe based on line number. # However the safe_halt() is a define rather than a function, so no # debug information exists for safe_halt() probe kernel.function("[EMAIL PROTECTED]/i386/kernel/process.c:114") { entries_halt_t = gettimeofday_us(); ++entries_halt; halt_state=1; } #interrupt is going to get it out of halted state probe kernel.function("irq_enter") { if (halt_state) { halt_state=0; exit_halt_t = gettimeofday_us(); ++exits_halt; stats_halt <<< exit_halt_t - entries_halt_t; } } probe end { stop_wall_time = gettimeofday_us(); runtime= stop_wall_time - start_wall_time; printf("Ran for %d us\n", runtime); printf("entered default_halt %d\n", entries_halt); printf("exited default_halt %d\n", exits_halt); /* print out some statistics on how much time spent halted */ if (@count(stats_halt)){ printf("percent halted: %d\n", @sum(stats_halt)*100/runtime); printf("count: %d\n", @count(stats_halt)); printf("avg_time: %d\n", @avg(stats_halt)); printf("min_time: %d\n", @min(stats_halt)); printf("max_time: %d\n", @max(stats_halt)); printf("usec distribution\n"); print (@hist_log(stats_halt)); } } _______________________________________________ Devel mailing list Devel@laptop.org http://mailman.laptop.org/mailman/listinfo/devel
