On Wed, Nov 26, 2025 at 02:20:14PM +0000, Mike Leach wrote:
[...]
* - timestamp
- Session local version of the system wide setting: :ref:`ETMv4_MODE_TIMESTAMP<coresight-timestamp>`
- Controls generation and interval of timestamps.0 = off, 1 = minimum interval .. 15 = maximum interval.Values 1 - 14 use a counter that decrements every cycle to generate atimestamp on underflow. The reload value for the counter is 2 ^ (interval- 1). If the value is 1 then the reload value is 1, if the value is 11then the reload value is 1024 etc.Setting the maximum interval (15) will disable the counter generatedtimestamps, freeing the counter resource, leaving only ones emitted whena SYNC packet is generated. The sync interval is controlled withTRCSYNCPR.PERIOD which is every 4096 bytes of trace by default.What is the default value?
From driver's pespective, the default value is 0 (disabled). We do set default values in perf: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tool...
IIUC, the default value would be the same with or without this series.
As far as I recall when this command line parameter was a bool then: perf -e cs_etm/timestamp/ <program> is sufficient to turn on timestamping.
Hmm... with the latest perf, we must assign value to `timestamp`, otherwise perf will report error:
# /mnt/build/perf record -e cs_etm/timestamp/ -C 0 -- taskset -c 0 ls event syntax error: 'cs_etm/timestamp/' ___ Bad event or PMU
Unable to find PMU or event on a PMU of 'cs_etm'
event syntax error: 'cs_etm/timestamp/' ___ no value assigned for term
event syntax error: 'cs_etm/timestamp/' ___ no value assigned for term Run 'perf list' for a list of valid events
This is worth mentioning so users can correctly assess what happens for any existing scripts they might have.
Based on this then the same command must set the timestamp to 1 - which will have the same effect as before as we do not want to break existing behaviour.
Mike
* - cc_threshold - Cycle count threshold value. If nothing is provided here or the provided value is 0, then the default value i.e 0x100 will be used. If provided value is less than minimum cycles threshold-- 2.34.1
-- Mike Leach Principal Engineer, ARM Ltd. Manchester Design Centre. UK