kprof - kernel profiling

 bind -a #T /dev  /dev/kpctl  /dev/kpdata 

The kprof device provides simple profiling data for the operating system kernel. The data accumulates by recording the program counter of the kernel at each `tick' of a profiling clock. Often this is just the system clock, but may be an independent higher priority timer which allows profiling of interrupt handlers, dependent on implementation.

The file kpdata holds the accumulated counts in big-endian byte order. The size of the file depends on the size of kernel text, and the size of the individual counts. The first six counts are 4 bytes in size, and are special. The first holds the total number of ticks, the second the number of ticks which fell outside the kernel text, the third the number of microseconds per tick, the fourth the number of sample buckets, the fifth the size in bytes of each sample bucket, and sixth the log base 2 of the sample bucket size. Typically the sample size is 4, and the log base 2 of the bucket size 3 (8 bytes). The remainder of the file holds the sample buckets. The entire file has size "sample bucket size" times "number of sample buckets" . That is, the first six sample buckets are replaced with the special numbers.

The file kpctl controls profiling. Writing the string start to kpctl begins profiling; stop terminates it. The message startclr restarts profiling after zeroing the array of counts.

Kprof (10.1) formats the data for presentation.

The following sh (1) commands define and invoke a function sample that runs a given test program with kernel profiling enabled, and copies the result to a server presumed to be mounted on /n/remote . .EX fn sample { echo start >/dev/kpctl $1 echo stop >/dev/kpctl cp /dev/kpdata /n/remote/tmp/kpdata } bind -a '#T' /dev sample {cp sound /dev/audio}

On the server, the kprof (10.1) command is used to analyse the data: .EX kprof /usr/inferno/os/mpc/impc /tmp/kpdata

/os/port/devkprof.c kprof (10.1) It cannot provide times for each node in the dynamic call graph (dynamic profiling).