To also trace kernel space presents a problem, namely kernel self-modifying
code. A fairly good kernel image is available in /proc/kcore but to get an
accurate image a copy of /proc/kcore needs to be made under the same conditions
-as the data capture. A script perf-with-kcore can do that, but beware that the
-script makes use of 'sudo' to copy /proc/kcore. If you have perf installed
-locally from the source tree you can do:
+as the data capture. 'perf record' can make a copy of /proc/kcore if the option
+--kcore is used, but access to /proc/kcore is restricted e.g.
- ~/libexec/perf-core/perf-with-kcore record pt_ls -e intel_pt// -- ls
+ sudo perf record -o pt_ls --kcore -e intel_pt// -- ls
-which will create a directory named 'pt_ls' and put the perf.data file and
-copies of /proc/kcore, /proc/kallsyms and /proc/modules into it. Then to use
-'perf report' becomes:
+which will create a directory named 'pt_ls' and put the perf.data file (named
+simply 'data') and copies of /proc/kcore, /proc/kallsyms and /proc/modules into
+it. The other tools understand the directory format, so to use 'perf report'
+becomes:
- ~/libexec/perf-core/perf-with-kcore report pt_ls
+ sudo perf report -i pt_ls
Because samples are synthesized after-the-fact, the sampling period can be
selected for reporting. e.g. sample every microsecond
- ~/libexec/perf-core/perf-with-kcore report pt_ls --itrace=i1usge
+ sudo perf report pt_ls --itrace=i1usge
See the sections below for more information about the --itrace option.