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Diffstat (limited to 'tools/perf/Documentation/intel-pt.txt')
| -rw-r--r-- | tools/perf/Documentation/intel-pt.txt | 59 |
1 files changed, 57 insertions, 2 deletions
diff --git a/tools/perf/Documentation/intel-pt.txt b/tools/perf/Documentation/intel-pt.txt index e0d9e7dd4f17..2cf2d9e9d0da 100644 --- a/tools/perf/Documentation/intel-pt.txt +++ b/tools/perf/Documentation/intel-pt.txt @@ -434,6 +434,56 @@ pwr_evt Enable power events. The power events provide information about "0" otherwise. +AUX area sampling option +------------------------ + +To select Intel PT "sampling" the AUX area sampling option can be used: + + --aux-sample + +Optionally it can be followed by the sample size in bytes e.g. + + --aux-sample=8192 + +In addition, the Intel PT event to sample must be defined e.g. + + -e intel_pt//u + +Samples on other events will be created containing Intel PT data e.g. the +following will create Intel PT samples on the branch-misses event, note the +events must be grouped using {}: + + perf record --aux-sample -e '{intel_pt//u,branch-misses:u}' + +An alternative to '--aux-sample' is to add the config term 'aux-sample-size' to +events. In this case, the grouping is implied e.g. + + perf record -e intel_pt//u -e branch-misses/aux-sample-size=8192/u + +is the same as: + + perf record -e '{intel_pt//u,branch-misses/aux-sample-size=8192/u}' + +but allows for also using an address filter e.g.: + + perf record -e intel_pt//u --filter 'filter * @/bin/ls' -e branch-misses/aux-sample-size=8192/u -- ls + +It is important to select a sample size that is big enough to contain at least +one PSB packet. If not a warning will be displayed: + + Intel PT sample size (%zu) may be too small for PSB period (%zu) + +The calculation used for that is: if sample_size <= psb_period + 256 display the +warning. When sampling is used, psb_period defaults to 0 (2KiB). + +The default sample size is 4KiB. + +The sample size is passed in aux_sample_size in struct perf_event_attr. The +sample size is limited by the maximum event size which is 64KiB. It is +difficult to know how big the event might be without the trace sample attached, +but the tool validates that the sample size is not greater than 60KiB. + + new snapshot option ------------------- @@ -487,8 +537,8 @@ their mlock limit (which defaults to 64KiB but is not multiplied by the number of cpus). In full-trace mode, powers of two are allowed for buffer size, with a minimum -size of 2 pages. In snapshot mode, it is the same but the minimum size is -1 page. +size of 2 pages. In snapshot mode or sampling mode, it is the same but the +minimum size is 1 page. The mmap size and auxtrace mmap size are displayed if the -vv option is used e.g. @@ -501,12 +551,17 @@ Intel PT modes of operation Intel PT can be used in 2 modes: full-trace mode + sample mode snapshot mode Full-trace mode traces continuously e.g. perf record -e intel_pt//u uname +Sample mode attaches a Intel PT sample to other events e.g. + + perf record --aux-sample -e intel_pt//u -e branch-misses:u + Snapshot mode captures the available data when a signal is sent e.g. perf record -v -e intel_pt//u -S ./loopy 1000000000 & |