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CYC packets are a new Intel PT feature.
CYC packets provide even finer grain timestamp information than MTC and
TSC packets. A CYC packet contains the number of CPU cycles since the
last CYC packet. Unlike MTC and TSC packets, CYC packets are only sent
when another packet is also sent.
Support for this feature is indicated by:
/sys/bus/event_source/devices/intel_pt/caps/psb_cyc
which contains "1" if the feature is supported and "0" otherwise.
CYC packets can be requested using a PMU config term e.g. perf record -e
intel_pt/cyc/u sleep 1
The frequency of CYC packets can also be specified. e.g. perf record -e
intel_pt/cyc,cyc_thresh=2/u sleep 1
CYC packets are not requested by default.
Valid cyc_thresh values are given by:
/sys/bus/event_source/devices/intel_pt/caps/cycle_thresholds
which contains a hexadecimal value, the bits of which represent valid
values e.g. bit 2 set means value 2 is valid.
The value represents the minimum number of CPU cycles that must have
passed before a CYC packet can be sent. The number of CPU cycles is:
2 ^ (value - 1)
e.g. value 4 means 8 CPU cycles must pass before a CYC packet can be
sent. Note a CYC packet is still only sent when another packet is sent,
not at, e.g. every 8 CPU cycles.
If an invalid value is entered, the error message will give a list of
valid values e.g.
$ perf record -e intel_pt/cyc,cyc_thresh=15/u uname
Invalid cyc_thresh for intel_pt. Valid values are: 0-12
tools/perf/Documentation/intel-pt.txt is updated in a later patch as
there are a number of new features being added.
For more information refer to the June 2015 or later Intel 64 and IA-32
Architectures SDM Chapter 36 Intel Processor Trace.
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/1437150840-31811-24-git-send-email-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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