diff options
Diffstat (limited to 'tools/perf/Documentation/perf-intel-pt.txt')
| -rw-r--r-- | tools/perf/Documentation/perf-intel-pt.txt | 55 |
1 files changed, 45 insertions, 10 deletions
diff --git a/tools/perf/Documentation/perf-intel-pt.txt b/tools/perf/Documentation/perf-intel-pt.txt index 456fdcbf26ac..f4cd49a7fcdb 100644 --- a/tools/perf/Documentation/perf-intel-pt.txt +++ b/tools/perf/Documentation/perf-intel-pt.txt @@ -69,22 +69,22 @@ And profiled with 'perf report' e.g. 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. @@ -687,7 +687,7 @@ The v4.2 kernel introduced support for a context switch metadata event, PERF_RECORD_SWITCH, which allows unprivileged users to see when their processes are scheduled out and in, just not by whom, which is left for the PERF_RECORD_SWITCH_CPU_WIDE, that is only accessible in system wide context, -which in turn requires CAP_SYS_ADMIN. +which in turn requires CAP_PERFMON or CAP_SYS_ADMIN. Please see the 45ac1403f564 ("perf: Add PERF_RECORD_SWITCH to indicate context switches") commit, that introduces these metadata events for further info. @@ -821,7 +821,9 @@ The letters are: e synthesize tracing error events d create a debug log g synthesize a call chain (use with i or x) + G synthesize a call chain on existing event records l synthesize last branch entries (use with i or x) + L synthesize last branch entries on existing event records s skip initial number of events "Instructions" events look like they were recorded by "perf record -e @@ -912,6 +914,39 @@ transactions events can be specified. e.g. Note that last branch entries are cleared for each sample, so there is no overlap from one sample to the next. +The G and L options are designed in particular for sample mode, and work much +like g and l but add call chain and branch stack to the other selected events +instead of synthesized events. For example, to record branch-misses events for +'ls' and then add a call chain derived from the Intel PT trace: + + perf record --aux-sample -e '{intel_pt//u,branch-misses:u}' -- ls + perf report --itrace=Ge + +Although in fact G is a default for perf report, so that is the same as just: + + perf report + +One caveat with the G and L options is that they work poorly with "Large PEBS". +Large PEBS means PEBS records will be accumulated by hardware and the written +into the event buffer in one go. That reduces interrupts, but can give very +late timestamps. Because the Intel PT trace is synchronized by timestamps, +the PEBS events do not match the trace. Currently, Large PEBS is used only in +certain circumstances: + - hardware supports it + - PEBS is used + - event period is specified, instead of frequency + - the sample type is limited to the following flags: + PERF_SAMPLE_IP | PERF_SAMPLE_TID | PERF_SAMPLE_ADDR | + PERF_SAMPLE_ID | PERF_SAMPLE_CPU | PERF_SAMPLE_STREAM_ID | + PERF_SAMPLE_DATA_SRC | PERF_SAMPLE_IDENTIFIER | + PERF_SAMPLE_TRANSACTION | PERF_SAMPLE_PHYS_ADDR | + PERF_SAMPLE_REGS_INTR | PERF_SAMPLE_REGS_USER | + PERF_SAMPLE_PERIOD (and sometimes) | PERF_SAMPLE_TIME +Because Intel PT sample mode uses a different sample type to the list above, +Large PEBS is not used with Intel PT sample mode. To avoid Large PEBS in other +cases, avoid specifying the event period i.e. avoid the 'perf record' -c option, +--count option, or 'period' config term. + To disable trace decoding entirely, use the option --no-itrace. It is also possible to skip events generated (instructions, branches, transactions) |